Haptic interface with variable modulation frequency

Abstract

The invention relates to a controller for driving an array of ultrasonic transducers capable of generating an acoustic field providing a tactile sensation at a distance, comprising: an input interface configured to receive a delay command (Cd) and a modulation command (Cm); for each ultrasonic transducer, a generator (7) of an actuation signal for the ultrasonic transducer, capable of being controlled by a control circuit (8) to deliver voltage pulses with a delay conforming to the delay command (Cd) and a modulation exploiting a modulating signal whose modulation frequency, which can take several values, is set by the modulation command (Cm); an output interface configured to provide the actuation signals to the ultrasonic transducers. Figure 4 (for the abstract)

Description

Title of the invention: Haptic interface with variable modulation frequency. Technical field

[0001] The field of the invention is that of human-machine interfaces using haptic effects that allow a user to interact with the environment through the sense of touch. The invention relates more particularly to interfaces generating an acoustic field capable of providing a tactile sensation at a distance. Previous technique

[0002] Mid-air haptics recreates the sensation of touch at a distance, thanks to an array of ultrasonic speakers that vibrate the user's skin. This technology can, for example, enhance immersion in video games, particularly through the addition of haptic effects when using virtual reality (VR), augmented reality (AR), or mixed reality (MR) headsets. It can also be used to enhance the functionality of automotive dashboards, providing the driver with haptic feedback while allowing them to keep their attention on the road.

[0003] Mid-air haptics uses an array of ultrasonic transducers excited at a frequency above 20 kHz, known as the carrier frequency, to generate a plurality of ultrasonic waves which, being inaudible, are focused into a predefined area of ​​space by manipulating the phase shift of the carriers, thus generating acoustic pressure. The carriers are modulated at low frequencies (typically between 10 Hz and 1000 Hz) so that the effect is perceptible to human mechanoreceptors.

[0004] EP 4 006 698 B1 patent describes a mid-air haptic interface that has several sub-arrays of ultrasonic transducers excited by different carrier frequencies to generate different haptic effects. This interface uses a single carrier modulation frequency.

[0005] US patent application 2018 / 0181203 Al discloses a mid-air haptic interface with identical carrier frequencies but different modulation frequencies, designed to stimulate different tactile receptors sensitive to different excitation frequencies and thus create a multipoint haptic effect. This patent application specifically describes fixed modulation frequencies of 50 Hz and 200 Hz, allowing a first focal point to be excited / unexcited every 20 ms and a second focal point to be excited / unexcited every 5 ms. In other words, this patent application discloses amplitude modulation of the carriers with a modulating square wave signal having a 50% duty cycle and a frequency of 50 Hz or 200 Hz. Description of the invention

[0006] The invention aims to provide an improved haptic interface capable of providing more complex sensations.

[0007] To this end, the invention proposes a controller for driving a set of ultrasonic transducers capable of generating an acoustic field providing a tactile sensation at a distance, comprising: - an input interface configured to receive a delay command and a modulation command; - for each ultrasonic transducer, a generator of an actuation signal for the ultrasonic transducer capable of being controlled by a control circuit to deliver voltage pulses with a delay respecting the delay command and a modulation exploiting a modulating signal whose modulation frequency, which is capable of taking several values, is fixed by the modulation command; - an output interface configured to provide actuation signals to ultrasonic transducers.

[0008] Some preferred but not limiting aspects of this controller are as follows: - the modulation control sets a modulation frequency common to all ultrasonic transducers; - the ultrasonic transducers are divided into several subsets of ultrasonic transducers and the modulation control sets a common modulation frequency for the transducers of a subset; - the distribution of ultrasonic transducers into several subsets of ultrasonic transducers is evolving over time; - the control circuit associated with each ultrasonic transducer is configured to generate the control logic signal in such a way as to perform pulse width modulation of the ultrasonic transducer actuation signal; - Pulse width modulation controls a duty cycle of the actuation signal from an amplitude of the modulating signal; - Pulse width modulation controls the duty cycle of the actuation signal based on the amplitude of the modulating signal during a rising edge of the actuation signal; - it includes at least one modulating signal generator circuit controlled by the modulation control. Brief description of the drawings

[0009] Other aspects, objectives, advantages and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0010] - [Fig. 1] is a diagram representing a system for supplying a sensation remote touchscreen according to the invention;

[0011] - Figure 2 illustrates the principle of focusing ultrasonic waves by playing on the phase shift;

[0012] - [Fig. 3] illustrates the possibility of generating different tactile sensations by coming vary the modulation frequency;

[0013] - [Fig. 4] is a diagram of a channel of a controller of a supply system of a tactile sensation at a distance in accordance with the invention;

[0014] - [Fig. 5] is a diagram illustrating the control of the transducers by means of n channels, each with independent variable modulation;

[0015] - [Fig. 6] is a diagram illustrating the control of the transducers by means of n channels with variable modulation common to several channels.

[0016] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0017] Figure 1 illustrates an example of a system 1 for providing a remote tactile sensation (or haptic interface) according to the invention. This system 1 comprises a set of ultrasonic transducers 2, for example carried by the same support 4, capable of generating an acoustic field providing a remote tactile sensation.

[0018] The system 1 also includes a data processing unit 6, for example a personal computer, responsible for generating commands 60 according to the position and the effect to be produced. These commands 60 are provided to a controller 3 responsible for controlling all the transducers. The controller 3 is specifically configured to shape the signals 30 sent to the transducers 2 in order to generate, with the ultrasonic waves emitted by the transducers, an acoustic pressure detectable by touch on a surface S, defined for example by the palm and / or fingers of a hand, in a focal zone F. The controller 3 can be a programmable logic circuit such as an FPGA. The commands 60 can be provided to it via a "UART over USB" connection.

[0019] In the example considered, the system 1 further comprises a detection system 5 configured to detect the position of the surface S to be tactilely stimulated and transmit corresponding location data 50 to the data processing unit 6.

[0020] The detection system 5 can be implemented with some of the transducers 2 that detect the position of the surface S by capturing the ultrasonic signal that reverberates off the surface S. Transducers with a frequency suitable for such capture can be dedicated to this function. Alternatively, any other A suitable detection system can be used, for example an optical detection system.

[0021] System 1 is of the mid-air type because the surface S to be tactilely stimulated is located at a distance from the transducers 2, and the focal zone F is located in the air at a distance from the transducers. The tactilely detectable acoustic pressures are generated according to a principle known as "acoustic electronic focusing," illustrated schematically in [Fig. 2]. To concentrate the ultrasonic waves 20 emitted by the transducers 2 into a predefined focal zone F, the control circuit 3 sends complex alternating signals 30 to the transducers 2 in a manner known per se. This introduces phase shifts between the different ultrasonic waves emitted by the actuated transducers 2, thus generating the desired wavefront shape. This wavefront shape results in an increase in acoustic pressure in the focal zone F.

[0022] In one embodiment, the transducers 2 are of the piezoelectric micromachined type (PMUT for "Piezoelectric Micromachined Ultrasonic Transducer"). Other types of transducers can be used interchangeably, for example electromagnetic actuators.

[0023] A single PMUT operating at a frequency of 100 kHz under 5V generates a sound pressure of approximately 0.15 Pa at 30 cm. Considering a voltage of 48V and assuming that the sound pressure increases linearly with the voltage, a sound pressure of approximately 1.44 Pa can be achieved with such a single PMU.

[0024] The threshold for feeling a haptic effect is around 200 Pa. By linearly adding the acoustic pressures, it follows that a matrix consisting of 139 transducers is required to obtain a haptic effect at 30 cm.

[0025] By way of example, the radius of the PMUT considered is on the order of 400 pm. Indeed, for a given frequency, the radius is related to the stiffness of the PMUT membrane, which is linked to its thickness and constituent materials. Considering a membrane spacing of 300 pm, which is sufficient to ensure the matrix's robustness while keeping the membranes close to each other, this results in a haptic matrix of the order of 1.5 x 1.5 cm² for 139 transducers.

[0026] In the context of the invention, the transducer array comprises a minimum number of transducers to obtain a haptic effect. This minimum number is 139 in the example considered here. A greater number of transducers is of course possible, particularly to ensure an effect over a greater distance. In particular, the transducers can be distributed among several subsets of transducers, each subset consisting of a number of transducers greater than this minimum number. By using several subsets, it is It is possible to create several simultaneous effects and thus offer a multi-point haptic interface. For example, two of a user's fingers can explore two zones independently of each other. Furthermore, the distribution of transducers within subsets can be dynamic, for example, depending on the location of the focal zone F.

[0027] The transducers can thus form a single set of transducers or, conversely, several subsets of transducers. In order for the generated acoustic pressure to be perceptible to the touch, low-frequency modulation of the carriers is implemented. The transducers in the single set have their actuation signals modulated at the same modulation frequency. Similarly, the transducers in a subset of transducers have their actuation signals modulated at the same modulation frequency. However, different modulation frequencies can be associated with the different subsets.

[0028] In the context of the invention, this same modulation frequency is variable. It is thus possible to obtain different haptic effects depending on the modulation frequency, in particular different texture effects.

[0029] Figure 3 illustrates a complex haptic effect that can be created using a variable modulation frequency. For a focal zone of type T1, the actuation signals are modulated with a low modulation frequency, advantageously between 10 and 200 Hz, providing the sensation of touching wood. For a focal zone of type T2, the actuation signals are modulated with an intermediate modulation frequency, advantageously between 200 Hz and 400 Hz, providing the sensation of touching a leaf. Finally, for a focal zone of type T3, the actuation signals are modulated with a high modulation frequency, advantageously between 400 and 800 Hz, providing the sensation of touching a bud.

[0030] It should be noted that the change in modulation frequency can be discrete or continuous. By gradually varying from one frequency to another, it is possible to generate a progressive effect, such as an effect providing an increasingly rough sensation.

[0031] A system 1 for providing a remote tactile sensation according to the invention, coupled with a detection system 5, can operate according to the following steps.

[0032] System 1 is first in standby mode, in the absence of a user (finger, hand or body part on which to generate a haptic effect) in the detection field of the detection system 5.

[0033] Subsequently, the detection system 5 detects the presence of a user's surface S in the detection field and locates the place(s) where the haptic effect(s) should be generated.

[0034] The data processing unit 6 then implements algorithms to determine the commands to be sent to the transducers 2 according to the position and the effect to be generated. In particular, the algorithm translates the effect to be generated into a suitable modulation frequency, for example a modulation frequency between 10 and 200 Hz to give the sensation of a rough material, a modulation frequency between 200 and 400 Hz to give the sensation of a smoother material, and a modulation frequency between 400 and 800 Hz to give the sensation of an even smoother material.

[0035] The data processing unit 6 here determines a delay command that is a function of the position of the focal zone F and a modulation command that is a function of the effect to be generated in this zone F. The delay command can take the form of a delay table indicating the delay to be applied to each of the actuation signals. The modulation command can take the form of a pulse table indicating the modulation frequency of each of the actuation signals.

[0036] These delay and modulation commands are provided to the controller 3, which in response shapes the transducer actuation signals to generate the desired haptic effect in the focal zone F. The delay command is used to apply a phase shift to the actuation signals in order to focus the ultrasonic waves at the focal zone. The modulation command, for its part, is used to modulate the actuation signals with a modulating signal whose modulation frequency, which can take several values, is set by the modulation control.

[0037] When the user moves out of the detection range of the detection system 5, the system goes back to standby.

[0038] The controller 3 thus has an input interface to receive the delay command and the modulation command generated by the data processing unit 6.

[0039] The controller 3 is of the multi-channel type with one channel dedicated to each ultrasonic transducer. Each channel includes a generator for the actuation signal of the corresponding transducer, this actuation signal being delayed according to the delay control and modulated according to the modulation control. The controller 3 further has an output interface for supplying the actuation signals thus generated to the ultrasonic transducers 2.

[0040] Figure 4 schematically represents such a channel 11 of the controller 3. This channel 11 includes a generator 7 for the actuation signal of the transducer associated with the channel and a control circuit 8. The generator 7 is a voltage pulse generator which is driven by a logic control signal generated by the circuit Control 8. When the control logic signal is in a first state, generator 7 provides a high-level voltage +HV, and when the control logic signal is in a second state, generator 7 provides a low-level voltage -HV. As an example, the +HV and -HV voltages are 3V and 0V respectively.

[0041] The control circuit 8 is configured to apply the control logic signal to the generator 7 in accordance with the delay control Cd and the modulation control Cm. The control logic signal enables the generator 7 to deliver voltage pulses with a delay respecting the delay control and a modulation exploiting a modulating signal whose modulation frequency, which can take several values, is set by the modulation control.

[0042] The control circuit includes a delay adjustment unit 9 driven by the delay control Cd (for example via the delay reported in a delay table for the transducer and the channel considered) and a pulse modulation unit 10 driven by the modulation control Cm (for example via the modulation frequency reported in a pulse table for the transducer and the channel considered).

[0043] In one possible embodiment, the pulse modulation unit 10 enables pulse-width modulation of the ultrasonic transducer actuation signal. For example, the delay adjustment unit 9 provides a pulse start indication (e.g., based on a rising edge), and the pulse modulation unit 10 provides a pulse duration indication. In particular, the pulse-width modulation controls the duty cycle of the actuation signal based on the amplitude of the modulating signal, the modulation frequency of which is set by the modulation control. For example, the pulse duration is a function of the amplitude of the modulating signal at the rising edge of the pulse.

[0044] From an electronic standpoint, pulse-width modulation has the advantage of not requiring the manipulation of analog signals. The controller outputs a signal that will have a state of 0 or 1 (for example, 0V and 3V). This signal is easily converted into a control voltage of several tens of volts for the transducers. Amplitude modulation, on the other hand, requires digital-to-analog conversion and analog amplification, which is costly in terms of both energy and price.

[0045] The controller 3 further includes at least one modulating signal generator circuit controlled by the modulation control Cm to deliver a modulating signal whose modulation frequency is set by the modulation control Cm.

[0046] When the set of transducers forms a single unit, the controller 3 can thus comprise a single modulating signal generator circuit controlled by The modulation control Cm. The transducers of the single assembly are modulated here at the same modulation frequency (the variable value of which is set by the modulation control). The modulation control here sets a common modulation frequency for all the ultrasonic transducers.

[0047] When the transducer array is divided into several transducer sub-arrays, the controller may include a signal generator circuit modulating each sub-array. The transducers in a sub-array are modulated at the same modulation frequency (the variable value of which is set by the modulation control), but the different sub-arrays may be modulated at different modulation frequencies. The modulation control sets a common modulation frequency for the transducers in a sub-array.

[0048] A combinational multiplexer can be used to route the value calculated by a modulating signal generator circuit to the channels of the corresponding subset of transducers.

[0049] Alternatively, time-division multiplexing can be implemented whereby each modulating signal generator circuit transmits in turn its identifier and the value it has calculated on a common bus, and each channel, previously associated with one of the generators, recognizes the address of the latter and records the corresponding calculated value.

[0050] The combinational multiplexer requires interfacing the elements, in particular connecting all the channel registers with all the output registers of the modulating signal generators. As the number of channels increases, this routing becomes extremely complex, and the combinational multiplexer becomes difficult to routable. By taking advantage of the difference between the operating frequency (which must be high, around one hundred MHz, to allow very fine adjustment of the delays) and the update frequency of the duty cycle values ​​(which is the carrier frequency, i.e., a few tens of kHz), it is possible to implement time-division multiplexing. This is slower, since the values ​​are transmitted one after the other, but because it is timed by the operating frequency, it is fast enough to be performed during a single carrier period.

[0051] Since the distribution of transducers in the sub-assemblies can be scalable, the controller 3 can also be provided with a modulating signal generator circuit for each channel, the transducers then being modulated independently. Figure 5 shows a schematic diagram of the computer 3 in this regard, where each channel 11 incorporates its own modulating signal computer. The computer 3 here performs shaping of the actuation signals with independent variable modulation.

[0052] Figure 6 shows a schematic diagram of the controller 3 for the previous case with a GSMb, GSMn, and GSMN modulating signal generator per subset (or group) of transducers. The computer 3 here performs signal conditioning of the actuation signals with variable modulation per group. The GSMb, GSMn, and GSMN modulating signal generators are not integrated within the channels 11.

[0053] In a preferred embodiment, the modulating signal is a sine wave, and the generator(s) deliver a sine wave whose modulation frequency is that set by the modulation control. The modulating signal generator(s) may take the form of pre-calculated sine wave tables for different modulation frequencies. Alternatively, the modulating signal generator(s) may be sine wave calculation circuits, such as CORDIC (Coordinate Rotation Digital Computer) circuits or LUTs (Look-Up Tables).

[0054] The invention extends to a device for generating an acoustic field providing a tactile sensation at a distance, comprising the controller 3 and a voltage converter capable of converting the actuation signals supplied by the controller into higher voltage signals. By way of example, the voltage converter is capable of delivering a 48V pulse from a 3V pulse. The voltage converter may, for example, have a half-bridge topology.

[0055] The invention is not limited to the controller, device and system described above but also extends to a method for controlling an array of ultrasonic transducers capable of generating an acoustic field providing a tactile sensation at a distance, comprising: - the receipt of a delay command and a modulation command; - the generation of transducer actuation signals in the form voltage pulses exhibiting a delay respecting the delay command and a modulation exploiting a modulating signal whose modulation frequency, which is capable of taking several values, is fixed by the modulation command; - the supply of modulated actuation signals to the ultrasonic transducers.

[0056] The invention also relates to a computer program product comprising instructions which, when the program is executed by a computer, lead the computer to implement this process.

Claims

Demands

1. Controller (3) for controlling an array of ultrasonic transducers (2) capable of generating an acoustic field providing a tactile sensation at a distance, comprising: - an input interface configured to receive a delay command (Cd) and a modulation command (Cm); - for each ultrasonic transducer, a generator (7) of an actuation signal for the ultrasonic transducer capable of being controlled by a control circuit (8) to deliver voltage pulses with a delay respecting the delay command (CD) and a modulation exploiting a modulating signal whose modulation frequency, which is capable of taking several values, is fixed by the modulation command (Cm); - an output interface configured to provide the actuation signals to the ultrasonic transducers (2).

2. Controller according to claim 1, wherein the modulation control sets a modulation frequency common to all ultrasonic transducers.

3. Controller according to claim 1, wherein the ultrasonic transducers are distributed into several subsets of ultrasonic transducers and wherein the modulation control sets a common modulation frequency for the transducers of a subset.

4. Controller according to claim 3, wherein the distribution of ultrasonic transducers into several subsets of ultrasonic transducers is time-evolving.

5. Controller according to any one of claims 1 to 4, wherein the control circuit associated with each ultrasonic transducer is configured to generate the control logic signal so as to achieve pulse width modulation of the ultrasonic transducer actuation signal.

6. Controller according to claim 5, wherein pulse width modulation controls a duty cycle of the actuation signal from an amplitude of the modulating signal.

7. Controller according to claim 6, wherein pulse-width modulation controls the duty cycle of the signal actuation from an amplitude of the modulating signal during a rising edge of the actuation signal.

8. Controller according to any one of claims 1 to 7, comprising at least one modulating signal generator circuit (GMb GMn, GMN) controlled by the modulation control.

9. Device for generating an acoustic field providing a tactile sensation at a distance, comprising a controller according to any one of claims 1 to 8 and a voltage converter capable of converting actuation signals into higher voltage signals.

10. System (1) for providing a remote tactile sensation, comprising: - an array of ultrasonic transducers (2); - a detector (5) configured to detect the position relative to the transducers of a user's surface to be tactilely stimulated; - a data processing unit (6) configured to generate a delay command and a modulation command as a function of the position of the user's surface thus detected; - a controller according to any one of claims 1 to 8.

11. A method for controlling an array of ultrasonic transducers capable (2) of generating an acoustic field providing a tactile sensation at a distance, comprising: - receiving a delay command (Cd) and a modulation command (Cm); - generating transducer actuation signals in the form of voltage pulses having a delay respecting the delay command and a modulation exploiting a modulating signal whose modulation frequency, which is capable of taking several values, is fixed by the modulation command; - supplying the modulated actuation signals to the ultrasonic transducers.

12. Product computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to claim 11.

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