Calibration and detection techniques in haptic systems

Abstract

Described is a system for producing an acoustic field from a plurality of ultrasonic transducer arrays, each of which has known relative positions and orientations. The acoustic field comprises a carrier wave and a modulated wave. The carrier wave has a plurality of modulated focal areas. A plurality of control points having a known spatial relationship relative to at least one of the plurality of ultrasonic transducer arrays is used. The plurality of ultrasonic transducer arrays are calibrated by using the relative position of each of the plurality of ultrasonic transducer arrays.

Description

FIELD OF THE DISCLOSURE

The present disclosure relates generally to improved calibration and detection techniques in haptic-based systems.

BACKGROUND

It is known to use a continuous distribution of sound energy, which will be referred to herein as an “acoustic field”, for a range of applications, including haptic feedback.

It is known to control an acoustic field by defining one or more control points in a space within which the acoustic field may be specified. Each control point is assigned an amplitude value equating to a desired amplitude of the acoustic field at the control point. Transducers are then controlled to create an acoustic field exhibiting the desired amplitude at each of the control points. When human skin interacts with the acoustic field, vibrations of the skin are interpreted by mechanoreceptors being excited and sending signals to the brain via the nervous system.

When used in mid-air, haptic technology works by focusing sound at an ultrasonic carrier frequency to a point or points in the space above the transducers. Then this is modulated by a waveform including low frequency content that generates the haptic sensation.

The behavior of ultrasonic acoustics is a well understood approach to range finding and positioning. Accordingly, due to the fact that the hardware requirement for ultrasonic haptic feedback significantly overlaps with that of ultrasonic positioning systems, the ability to build arrays with positioning capabilities in haptic systems is advantageous.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.

FIG. 1 shows a first simulation of a set of ultrasonic transducers emitting output at a monochromatic ultrasonic carrier frequency.

FIG. 2 shows a second simulation of a set of ultrasonic transducers emitting output at a frequency-modulated ultrasonic carrier frequency.

Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION

I. Background

A method of producing an acoustic field using an array of transducers having known relative positions and orientations may include

defining a plurality of control points which each have a known spatial relationship relative to the array of transducers;

assigning an amplitude to each control point;

computing a matrix containing elements which represent, for each of the control points, the effect that producing a modeled acoustic field having the assigned amplitude with a particular phase at the control point has on the consequential amplitude and phase of the modeled acoustic field at the other control points;

determining eigenvectors of the matrix, each eigenvector representing a set of phases and relative amplitudes of the modeled acoustic field at the control points;

selecting one of the sets and operating the transducer array to cause one or more of the transducers to output an acoustic wave each having an initial amplitude and phase such that the phases and amplitudes of the resultant acoustic field at the control points correspond to the phases and relative amplitudes of the selected set.

A control point is a marker at a particular location. The distance between adjacent control points should be sufficient to enable the sound waves of the acoustic field to phase shift from one of the control points to match the next control point. In some embodiments the separation distance may be equal to the wavelength of the sound waves of the acoustic field.

Thus, an aspect of the system includes formulating an eigenproblem which can be solved to find valid phases at the control points. Use of an eigenproblem in the embodiments of the invention results in a faster and more predictable solution time in comparison with known methods, which in turn means that a higher number of control points can be supported, and may enable real-time updating of the control points. The eigenproblem does not in itself change the solution time but aids the solution through the modification of the phase relationships between control points. A faster and more predictable solution time also means that an acoustic field of larger volume can be controlled in comparison to known methods.

In embodiments of the invention a transducer array comprises one or more transducers in any suitable configuration; for example, one or more two dimensional arrays arranged in parallel.

The modelled acoustic field which has the assigned amplitude and a particular phase at a control point may be modelled as being produced by a virtual transducer directly below the control point. In some embodiments the virtual transducer may be in the in the plane of the real transducer array. However, the skilled person will appreciate the acoustic field may be modelled as being produced by other arrangements of virtual transducers, that is one or more virtual transducers which may be positioned directly below the control point or may have a different spatial relationship to the control point may be used to produce the modelled acoustic field. The use of virtual transducers enables a lookup table to be pre-computed. Preferably, the virtual transducers match the transducers of the transducer array.

The method may include the step of calculating eigenvalues of the matrix. The eigenvalues represent scaling factors, some of which will be relatively high and some of which will be relatively low, in relation to each other. The method may comprise selecting a set of phases and relative amplitudes with a relatively high corresponding eigenvalue as the selected set. Preferably, the method may comprise selecting the set of phases and relative amplitudes with the highest corresponding eigenvalue as the selected set.

The eigenvalues define how the corresponding eigenvectors scale when they are transformed by the matrix. That is, the eigenvalues represent how much the relative amplitudes of the acoustic field at the control points will scale up once the indirect contributions to the amplitude at each control point caused by producing an assigned amplitude at the other control points is taken into account. Therefore, finding a large eigenvalue indicates a corresponding set of relative amplitudes and phases that make use of a large amount of constructive interference. Choosing a set of relative amplitudes and phases with a corresponding eigenvalue which is relatively high, taking into account the relative values of all the eigenvalues of the matrix, therefore has an advantage over choosing a relatively low eigenvalue, as it makes more efficient use of the power output by the transducers.

The method may include computing the effect of producing the assigned amplitude at one of the control points on the amplitude and phases at each of the other control points using a look-up function which defines how the amplitude and phase of the acoustic waves varies spatially due to attenuation and propagation. The look-up function may take into account one or both of two sources of amplitude and phase variation. Firstly, attenuation of the amplitude of acoustic waves output by a transducer, which increases with distance from the transducer, and secondly, the changes in phase that occur as the acoustic waves propagate through space.

If such a look-up function is used, the spatial variation of the phase of the sound waves due to attenuation and propagation only needs to be computed once for a particular transducer array, which decreases the time needed to model the acoustic field and the time needed to calculate the initial amplitude and phases of the transducers that will produce the phases and amplitudes of the resultant acoustic field.

The positions of the control points may be chosen to define parts of a virtual three-dimensional shape which occupies a volume in the acoustic field. For example, the control points may lie on the edges of the shape or adjacent to the edges of the shape or within the volume of the shape. The control points may define the whole of the shape, or more preferably a part of the shape. For example the control points may define a shape to be felt by a user as part of a haptic feedback system of which only the part of the shape with which the user is interacting may need to be defined, or the shape may be the shape of a product having points of interest on which an acoustic radiation force may be focused for manufacturing applications such as drying glue.

Providing a group of control points at which the acoustic field has a relatively high amplitude and a group of control points at which the acoustic field has a relatively low amplitude to provide a gradient in amplitude of the acoustic field at the edge of a virtual shape provides an advantage in haptic feedback applications since it produces a more detectable difference in amplitude of the acoustic field, rendering the edge of the virtual shape more easily detectable by a user. Also, in the case of haptic feedback, the relatively low amplitude control points can ensure that the parts of a user's hand that are not in contact with the shape cannot feel residual ultrasound surrounding the shape. In the absence of the low amplitude control points, the ultrasound at those points is not controlled and so there may be some constructive areas that the hand can feel.

At least some of the control points may be positioned at points where an object intersects with the virtual shape. At least some of the control points may be positioned adjacent to the points of intersection.

Positioning the control points at points in the region of where an object, for example a user's hand, intersects the virtual shape provides the advantage that the acoustic field only needs to be controlled at points on the virtual shape with which the object is interacting, which enables higher amplitudes to be produced at those control points. The points where the object intersects with the virtual shape may be monitored in real time by an object tracker, and control points may be positioned at different points in the acoustic field in response to the object position.

II. Multiple Array Configurations

In the event of multiple arrays being used in a single setup, there are a number of required calibration steps that may be automated effectively using positioning capabilities. Arrays will often be erroneously offset in time or space due to manufacturing imprecision or system clock differences. By correlating the output of an array of ultrasonic transducers employed as sources, which has been provided as input to sensors on another and given that the input signals are known, using a time difference of arrival (TDOA) algorithm the lag in time and space can be determined. TDOA is an electronic technique used in direction finding and navigation, in which the time of arrival of a specific signal, at physically separate receiving stations with precisely synchronized time references, are calculated This can be also used to provide an alternative method of compensation for time offsets, which could for example be caused by clock drift.

Determining differences in time and space may be used to initialize newly connected devices in a dynamic way, allowing them to add to the existing volumetric acoustic field in space which may be shared. Alternatively, if the devices are freely movable or can move while constrained by a hinge, for example, this movement can be automatically detected and compensated for as the movement happens, providing no loss of feedback even when multiple arrays are in motion relative to one another. This may also be used to synchronize arrays to a common space, which includes an input sensor so that they can act as a single interactive volume.

III. Chirping Using Focus Points

The ultrasonic haptic feedback technology works purely on the monochromatic behavior of phase and amplitude from each transducer. Traditional sonar as well as the echolocation used by animals often contains frequency-modulated content to pick out individual reflections from objects encountered in the scene. The production of the acoustic haptic feedback relies on constant frequency output. For a given focus point each part of the amplitude modulated wave can be delayed such that the waves arrive at the focus point simultaneously. In order to preserve the haptic feedback the waves generally should be monochromatic, but this requirement can be potentially relaxed. The waves only need to be monochromatic at the point in time and space where they interact to generate a focus point. This suggests that the carrier frequency of the waves may be frequency modulated in time, as long as at the point they reach the focus, the carrier frequency is the same. Thus if the carrier frequency is modulated and delayed in the same way as the amplitude modulated content, then focusing may be achieved while continuously modifying the carrier frequency. At this point the carrier frequency may be modified into a chirp, or a range of frequencies that can be used to, given a set of microphones, locate objects in the acoustic field without changing the haptic effect of the transducer array. (A chirp is a signal in which the frequency increases (up-chirp) or decreases (down-chirp) with time.)

Shown in FIG. 1 is a first simulation 10 of a set of ultrasonic transducers 13, emitting output at a monochromatic ultrasonic carrier frequency 12 that has been focused to a point 11. Shown in FIG. 2 is a second simulation 20 of ultrasonic transducers 23 that are emitting a frequency-modulated ultrasonic carrier signal 22 that remains focused at the same point 21, due to the frequency modulation being offset in time such that the focusing remains functioning.

IV. Virtual Acoustic Point Sources

When generating the haptic effects, a focused control point in space is modulated with a low frequency vibration, usually consisting of one or more frequencies ranging from 0 Hz up to 500 Hz order to provide haptic feedback in the case of an amplitude modulated point. For other haptic techniques this may not be necessary and be replaced by some form of spatio-temporal modulation. Further, processed audio signals with components ranging from 100 Hz up to 20 kHz may be amplitude modulated on top of the points to provide the equivalent of parametric audio.

Modulating near-ultrasonic and ultrasonic tracking signals into each control point to create further virtual acoustic sources in mid-air, in the same position as the control points can be achieved. These sources would be reflected from objects in the field allowing existing sonar, range-finding and acoustic imaging techniques to function by applying a filter to received signals such that only the tracking signals are recovered. These tracking signals may be implemented in practice as modulation by amplitude, phase, frequency or quadrature, so long as this achieves a resulting modulation that substantially fits within bands of acoustic frequencies above the range of human hearing. Alternatively, the tracking signal may be audible, but designed to be unobtrusive in audible frequencies, which could be achieved by designing it to have similar properties to a random noise function. The tracking waveform associated with each control point should be distinct in frequency components and/or a signal made up of suitably orthogonal functions so that it may be picked out of the mix of frequencies expressed at the control point. Using further frequencies on top of each control point allows the tracking to continue to function even during periods of device activity.

A second active scan mode is also possible, which may be also used when the haptics is not enabled, which uses low power control points modulated only with the tracking signal. In this way, the device can continue to explore space, collecting imaging and ranging data in order to detect and pinpoint potential interactions. This active scan mode may also be used alongside haptics to create tracking control points separately to, but alongside, haptic control points.

A further advantage to using a virtual source to produce the tracking signal through a control point is that the system becomes robust to obscuring obstacles. In the case that output from a selection of the physical source transducers is blocked, the remaining transducers will remain contributing to the control point and thus the virtual source. The control point may also undergo movement allowing obstacles to be avoided.

The device may also be configured to ensure that the phases of the frequencies produced in the tracking signal are replicated correctly at the control point to reproduce the virtual source with enough fidelity. Also necessary to determine the time of flight is to monitor the delta time from emission to the moment of focussing in order to correctly find when the tracking signal is ‘emitted’ from the virtual source in the control point. Time of flight (TOF) describes a variety of methods that measure the time that it takes for an object, particle or acoustic, electromagnetic or other wave to travel a distance through a medium. This measurement can be used for a time standard (such as an atomic fountain), as a way to measure velocity or path length through a given medium, or as a way to learn about the particle or medium (such as composition or flow rate). The traveling object may be detected directly (e.g., ion detector in mass spectrometry) or indirectly (e.g., light scattered from an object in laser doppler velocimetry). From that point, the virtual source position, timings and emitted waves are known, and so traditional techniques for determining time of flight from the single virtual source to one or many receivers may be used to triangulate reflections and image the space.

V. CONCLUSION

The various features of the foregoing embodiments may be selected and combined to produce numerous variations of improved haptic systems.

In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings.

The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has”, “having,” “includes”, “including,” “contains”, “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially”, “essentially”, “approximately”, “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.

Claims

1. A method comprising: i) producing an acoustic field from a plurality of ultrasonic transducer arrays, each of which has known relative positions and orientations, wherein the acoustic field comprises a carrier wave and a modulated wave, wherein the carrier wave has a plurality of modulated focal areas and wherein the carrier wave is used to locate an object within the acoustic field;ii) defining a plurality of mid-air control points wherein each of the plurality of mid-air control points has a known spatial relationship relative to at least one of the plurality of ultrasonic transducer arrays;iii) for at least one of the plurality of mid-air control points, replicating phases of frequencies produced in the carrier wave and creating a haptic effect by amplitude-modulating the mid-air control point with a signal comprised of at least one frequency less than 20 KHz.

2. The method as in claim 1, wherein all frequencies are less than 20 KHz within the signal comprised of at least one frequency less than 20 KHz signal.

3. The method of claim 1, wherein the modulated wave uses amplitude modulation to produce parametric audio at a frequency audible to humans at the at least one of the plurality of mid-air control points.

4. The method of claim 1, wherein the object has object properties and the carrier wave is used to measure the object properties.

5. The method of claim 4, wherein the measurement of the object properties uses phases of the frequency of the carrier wave.

6. The method of claim 5, wherein the measurement of the object properties also uses a time-of-flight determination.

7. A method comprising: i) producing an acoustic field from a plurality of ultrasonic transducer arrays, each of which has known relative positions and orientations, wherein the acoustic field comprises a carrier wave and a modulated wave, wherein the carrier wave has a plurality of modulated focal areas and the carrier wave is used to locate an object within the acoustic field;ii) defining a plurality of mid-air control points wherein each of the plurality of mid-air control points has a known spatial relationship relative to at least one of the plurality of ultrasonic transducer arrays;iii) for at least one of the plurality of mid-air control points, replicating phases of frequencies produced in the carrier wave and creating a haptic effect using amplitude-modulation the mid-air control point with a signal comprised of at least one frequency less than 20 KHz.

8. The method of claim 7, wherein the modulation is spatio-temporal modulation.

9. The method of claim 7, wherein the object has object properties and the carrier wave is used to measure the object properties.

10. The method of claim 9, wherein the measurement of the object properties uses phases of the frequency of the carrier wave.

11. The method of claim 10, wherein the measurement of the object properties also uses a time-of-flight determination.