Measurement system and head-mounted display

Abstract

This measurement system (1) comprises: a first transmission element (10) that generates a first sound wave (SS1) for transmission; a first reception element (20) that receives second sound waves (RS1-RS3), which result when the first sound waves (SS1) are reflected by an object; and a signal processing unit (30) that causes the first transmission element (10) to transmit the first sound wave (SS1) and receives a first reception signal (SR1) corresponding to the second sound waves (RS1-RS3) from the first reception element (20). The signal processing unit (30) is configured to calculate the distance to the object on the basis of the latest time when the amplitude of the first reception signal (SR1) exceeds a determination value within a fixed period from the time when the first sound wave (SS1) is emitted.

Description

Measurement system and head-mounted display

[0001] The present disclosure relates to a measurement system and a head-mounted display.

[0002] Ranging systems that measure distance using the Time of Flight (TOF) of acoustic waves are already in practical use. The simplest ranging system consists of a transmitting element and a receiving element, or a transmitting and receiving element that functions both as a transmitter and a receiver, and a signal processing unit. The ranging system measures the distance to an object based on the time when the acoustic wave is transmitted and the time when the receiving element receives the acoustic wave reflected from the object.

[0003] In addition, by arranging two or more receiving elements, it can be used as a position detection system that detects not only the distance but also the position of an object. Based on the difference in the time when each receiving element detects the reflected wave, the position of the object in two-dimensional or three-dimensional space can be measured.

[0004] Distance measurement systems are widely used as obstacle detection systems for vehicles, etc. They are also used in gesture sensors. For example, by measuring the distance to a hand and assigning an action according to the distance, non-contact operations such as turning a device on / off and adjusting the volume become possible.

[0005] A device employing such a distance measurement system is disclosed in Japanese Patent Application Laid-Open No. 2005-266840. This device uses a transmitting means composed of an electromagnetic wave transmitting circuit, an ultrasonic wave transmitting circuit, and a trigger transmitting circuit. Three-dimensional spatial position information is determined from transmission and reception distance information obtained using two transmitting means with different propagation speeds, and position information and distance information obtained from multiple receiving means. When an operator moves the transmitting means, the cursor displayed on a display device such as a personal computer also moves in tandem. Furthermore, by providing the transmitting means with multiple switches as trigger generating means, it is possible to perform operations such as clicking and dragging.

[0006] Japanese Patent Application Laid-Open No. 2005-266840

[0007] Ranging systems generally calculate distance based on the first signal received. Therefore, distance detection is limited to the distance to the object closest to the receiving sensor. Furthermore, in the case of gesture sensors in head-mounted display (HMD) devices, such as AR / VR goggles, which have a goggle-like shape, sound waves are reflected not only from the hand but also from the arm. This makes it difficult to accurately measure the distance to the hand, making non-contact operation using hand movements difficult.

[0008] The present disclosure is made to explain an embodiment that solves the above-mentioned problems, and its purpose is to provide a measurement system that can measure the distance to an object, such as a hand or arm, that is located closer than the sensor.

[0009] The present disclosure relates to a measurement system. The measurement system includes a first transmitting element that generates a first sound wave to be transmitted, a first receiving element that receives a second sound wave that is reflected from an object, and a signal processing unit that causes the first transmitting element to transmit the first sound wave and receives a first received signal corresponding to the second sound wave from the first receiving element. The signal processing unit is configured to calculate the distance to the object based on the latest time at which the amplitude of the first received signal exceeds a threshold value within a certain period of time from the time the first sound wave is emitted.

[0010] According to the measurement system of the present disclosure, the distance to the target is calculated based on the latest time at which the amplitude of the first received signal exceeds the threshold within a certain period of time from the time the first sound wave is emitted, so that the distance to a target such as a hand that is close to the sensor can be measured appropriately even if the non-detection target object, such as an arm, is located close to the sensor.

[0011] FIG. 1 is a diagram illustrating the configuration of a measurement system of a first embodiment. FIG. 2 is a diagram illustrating sound waves transmitted by a transmitting element and received by a receiving element. FIG. 3 is a diagram illustrating a transmitted signal. FIG. 4 is a diagram illustrating a received signal. FIG. 5 is a diagram illustrating an example in which the measurement system of the first embodiment is applied to an HMD. FIG. 6 is a diagram illustrating the configuration of a measurement system of a second embodiment. FIG. 7 is a layout diagram illustrating how the position of an object is identified in the measurement system of the second embodiment. FIG. 8 is a waveform diagram illustrating how the position of an object is identified in the measurement system of the second embodiment. FIG. 9 is a diagram illustrating an example in which the measurement system of the second embodiment is applied to an HMD. FIG. 10 is a diagram illustrating the configuration of a measurement system of a third embodiment. FIG. 11 is a diagram illustrating an example in which the measurement system of the third embodiment is applied to an HMD. FIG. 12 is a diagram illustrating how the positions of both hands are detected using the measurement system of the third embodiment.

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. While several embodiments will be described below, it was originally intended that the configurations described in each embodiment be combined as appropriate. Note that identical or corresponding parts in the drawings will be designated by the same reference numerals, and their description will not be repeated.

[0013] Embodiment 1. Fig. 1 is a diagram showing the configuration of a measurement system according to embodiment 1. Fig. 2 is a diagram for explaining sound waves transmitted by a transmitting element and received by a receiving element.

[0014] The measurement system 1 shown in Fig. 1 includes a transmitting element 10, a receiving element 20, and a signal processing unit 30. As shown in Fig. 2, the transmitting element 10 generates a transmitted sound wave SS1. The receiving element 20 receives reflected sound waves RS1 to RS3 from objects J1 to J3.

[0015] The signal processing unit 30 is configured to generate a transmission signal for causing the transmitting element to emit a sound wave SS1, and to process a reception signal corresponding to the sound wave received by the receiving element 20. As the transmitting element 10 and the receiving element 20, a single transmitting / receiving element that functions both as a transmitter and a receiver may be used.

[0016] Fig. 3 is a diagram showing a transmission signal. Fig. 4 is a diagram showing a received signal. The transmission signal shown in Fig. 3 corresponds to the sound wave SS1, and time ts is the time when transmission starts.

[0017] The transmission signal can be, for example, a sine wave burst signal. In Figure 3, the transmission time ts is set to the start time of issuing the transmission signal, but since the width of the transmission signal is sufficiently short compared to the width of the received signal, the transmission time ts can also be set to the center or end of the burst signal. Various adjustments can be made to these.

[0018] FIG. 4 also shows received signals corresponding to sound waves RS1, RS2, and RS3 that are the result of the sound wave SS1 being reflected by objects J1, J2, and J3.

[0019] In general distance detection, the distance to the closest object is calculated by TOF based on the earliest time ti at which a certain signal magnitude (determination value St) is exceeded.

[0020] In contrast, in this embodiment, the distance d is calculated based on the latest time tf at which a certain signal magnitude (criterion value St) is exceeded within a certain time period (ts to tm) from the transmission time. The distance d can be calculated using, for example, the following formula (1): d = (tf - ts) / 2C (1) where d, ts, and C represent the distance to the farthest object within a certain area, the transmission time, and the speed of sound, respectively. "Within a certain area" refers to an area centered on the transmitting and receiving element, with a radius equal to half the distance sound travels from the transmission time ts to time tm within the certain time period. However, the above formula (1) is only an example of a calculation formula, and corrections may be made due to delays in signal processing, etc.

[0021] As explained above, in this embodiment, the distance to the object is calculated by taking the latest time tf at which the signal exceeds a certain signal magnitude (criterion value St) within a certain time period (ts to tm) as the sound wave reception time, as shown in Figure 4. As a result, sound waves RS1 and RS2 reflected by closer objects J1 and J2 do not affect the distance detected by the measurement system.

[0022] Therefore, it is possible to measure the distance to the farthest object within a region within a certain distance from the measurement system as the starting point.

[0023] 5 is a diagram showing an example in which the measurement system of the first embodiment is applied to an HMD 100. When a distance detection system is installed in an HMD, it is difficult to accurately detect the distance to the hand using a general method for detecting the distance and position of the closest object due to reflection from the arm. For example, when an HMD is worn and the arm is extended, the detected waveform will show a peak in the area where the reflection is strong on the arm, resulting in a waveform like that shown in FIG. 4. As a result, the position of the palm cannot be accurately detected using a general method.

[0024] In the HMD 100, a detection target, such as a hand, is located beyond the screen viewed by the user. In other words, the screen and the sensor transmission / reception unit are disposed between the user's eyes and the detection target. By applying the method for detecting the distance to the farthest target within a certain area, as described in the first embodiment, to an HMD with such an arrangement, it becomes possible to detect the distance of the hand located at the farthest position from the HMD 100. For example, if the distance of an average person's outstretched arm is 1 meter, the "within a certain area" may be an area with a radius of approximately 1 meter from the HMD 100. This allows the HMD 100 to be operated, such as by turning it on / off or adjusting the volume, depending on the distance to the hand.

[0025] For example, if objects J1 and J2 are associated with the arms and object J3 is associated with the hand, the latest time tf at which the signal exceeds a certain signal magnitude (determination value St) in the waveform of Figure 4 is taken as the sound wave reception time, and the distance to the object is calculated, thereby making it possible to measure the distance to the hand without the influence of the arm.

[0026] Embodiment 2 In embodiment 2, two or more receiving elements are arranged in the measurement system described in embodiment 1, and the position of the farthest object within a certain area is detected from the difference in the reception time of the reflected sound waves from each receiving element.

[0027] Fig. 6 is a diagram showing the configuration of a measurement system according to embodiment 2. The measurement system 101 shown in Fig. 6 includes a first transmitting element 110 that generates a first sound wave SS1 to be transmitted, a first receiving element 121 that receives second sound waves RS1 to RS3 that are reflected from the first sound wave SS1 by an object, and a signal processing unit 130 that causes the first transmitting element 110 to transmit the first sound wave SS1 and receives a first received signal SR1 corresponding to the second sound waves RS1 to RS3 from the first receiving element 121. The above configuration is the same as that of embodiment 1.

[0028] 6 further includes a second receiving element 122 that is disposed at a different position from the first receiving element 121 and receives a second sound wave. The signal processing unit 130 receives a second receiving signal SR2 corresponding to the second sound wave from the second receiving element 122, and detects the position of the object based on the first receiving signal SR1 and the second receiving signal SR2.

[0029] While the two-dimensional position can be determined as described above, the measurement system 101 shown in Figure 6 further includes a third receiving element 123 that is positioned differently from the first receiving element 121 and the second receiving element 122 and receives a second sound wave. The signal processing unit 130 receives a third receiving signal SR3 corresponding to the second sound wave from the third receiving element 123 and detects the position of the object based on the first receiving signal SR1, the second receiving signal SR2, and the third receiving signal SR3. This makes it possible to determine the three-dimensional position.

[0030] In the above configuration, a portion that transmits and receives signals ST1, SR1 to SR3 to and from signal processing portion 130 is defined as position detection portion TR1. Position detection portion TR1 includes transmitting element 110 and receiving portion 120. Receiving portion 120 includes receiving elements 121 to 123.

[0031] Fig. 7 is a layout diagram for explaining how to identify the position of an object in the measurement system of embodiment 2. Fig. 8 is a waveform diagram for explaining how to identify the position of an object in the measurement system of embodiment 2. For simplicity of explanation, Figs. 7 and 8 explain how to identify a two-dimensional position using two receiving elements 121 and 122.

[0032] 7, if the distance between receiving element 121 and receiving element 122 is sufficiently short compared to the distance to the object, the farthest object detected by receiving element 121 and the farthest object detected by receiving element 122 will be the same object J3. Therefore, the position (x, y) of object J3 can be identified from distance d1 and distance d2.

[0033] As shown in Figures 7 and 8, the signal processing unit 130 is configured to calculate the distance d1 to the object J3 based on the latest time tf1 at which the amplitude of the first received signal SR1 exceeds the judgment value St within a certain time tm from the time ts2 at which the first sound wave SS1 is emitted.

[0034] Furthermore, the signal processing unit 130 is configured to calculate the distance d2 to the object J3 based on the latest time tf2 at which the amplitude of the second received signal SR2 exceeds the judgment value St within a certain time tm from the time ts2 at which the first sound wave SS1 is emitted.

[0035] The principle of position detection will now be explained. An example of calculating the position of the farthest object within a certain area when two receiving elements are arranged is shown in FIGS. 6 and 7. The distances d1 and d2 from receiving element 121 and receiving element 122 to the farthest object within a certain area can be calculated using the following equations (2) and (3) using the same method as in embodiment 1. d1=(tf1-ts) / 2C ... (2) d2=(tf2-ts) / 2C ... (3) A circle with radius d1 centered on receiving element 121 and a circle with radius d2 centered on receiving element 122 intersect at a single point on a plane in the forward direction, so the position (x, y) of the farthest object within a certain area in two-dimensional space can be identified.

[0036] When three or more elements are arranged, it is also possible to detect the position within three-dimensional space. The time tf3 and detection distance d3 corresponding to receiving element 123 can be similarly calculated using the following formula (4): d3 = (tf3 - ts) / 2C ... (4) In three-dimensional space, a sphere with a radius d1 centered on receiving element 121, a sphere with a radius d2 centered on receiving element 122, and a sphere with a radius d3 centered on receiving element 123 intersect at a single point in three-dimensional space, as long as it is limited to the forward direction, and therefore the position (x, y, z) of the farthest object within a certain area within three-dimensional space can be identified.

[0037] 9 is a diagram showing an example in which the measurement system of the second embodiment is applied to an HMD 200. When a position detection system is installed in an HMD, it is difficult to accurately detect the position of the hand due to reflection from the arm using a general method for detecting the distance or position of the nearest object.

[0038] In an HMD, a detection target, such as a hand, is located beyond the screen viewed by the user. In other words, the screen and the sensor transmission / reception unit are disposed between the user's eyes and the detection target. For an HMD with such a configuration, this embodiment applies the method for detecting the position of the farthest target within a certain area described in the first embodiment, thereby making it possible to detect the position of the hand located farthest from the HMD 100. For example, assuming that the distance of an average person's outstretched arm is 1 meter, this "within a certain area" may be within a radius of approximately 1 meter from the HMD 200. This allows, for example, a change in the position of the hand to change the position of a pointer displayed on the HMD display and perform operations such as swiping the screen.

[0039] For example, objects J1 and J2 are associated with the arms, and object J3 is associated with the hand. By calculating the distance to the object using the latest time tf1 at which the waveform of the received signal SR1 in Figure 8 exceeds a certain signal magnitude (criterion value St) as the sound wave reception time, it is possible to measure the distance d1 to the hand without the influence of the arm.

[0040] Similarly, by calculating the distance to the object using the latest time tf2 at which the waveform of the received signal SR2 in Figure 8 exceeds a certain signal magnitude (determination value St) as the sound wave reception time, the distance d2 to the hand can be measured without the arm having any effect.

[0041] Although not shown in the figure, by calculating the distance to the object using the latest time tf3 at which the waveform of the received signal SR2 exceeds a certain signal magnitude (determination value St) as the sound wave reception time, the distance d3 to the hand can be measured without the influence of the arm.

[0042] If the distances d1, d2, and d3 can be calculated, the position of the hand can be identified. Embodiment 3 In embodiment 3, two or more position detection units are arranged in the measurement system described in embodiment 2, and the positions of the farthest object in the first area and the farthest object in the second area are detected from the difference in the reception times of the reflected sound waves by each receiving element.

[0043] Fig. 10 is a diagram showing the configuration of a measurement system according to embodiment 3. Fig. 11 is a diagram showing an example in which the measurement system according to embodiment 3 is applied to an HMD. Fig. 12 is a diagram showing how the positions of both hands are detected using the measurement system according to embodiment 3.

[0044] The measurement system 201 shown in FIG. 10 includes a position detection unit TR1, a position detection unit TR2, and a signal processing unit 250.

[0045] The position detection unit TR1 includes a transmitting element 210 that generates a sound wave SS11 to be transmitted, and a receiving unit 220 that receives sound waves RS11 to RS13 that are the sound waves SS11 reflected by an object. The receiving unit 220 includes a receiving element 221, a receiving element 222, and a receiving element 223.

[0046] The signal processing unit 250 causes the transmitting element 210 to transmit a sound wave SS11, receives a receiving signal SR11 corresponding to the sound waves RS11 to RS13 from the receiving element 221, receives a receiving signal SR12 corresponding to the second sound waves RS1 to RS3 from the receiving element 222, and receives a receiving signal SR13 corresponding to the sound waves RS1 to RS3 from the receiving element 223.

[0047] The above configuration is the same as that of embodiment 3. In addition, the measurement system 201 also receives reception signals SR21 to SR23 from the position detection unit TR2.

[0048] The position detection unit TR2 includes a transmitting element 230 that generates a sound wave SS12 to be transmitted, and a receiving unit 240 that receives sound waves RS14 to RS16 that are the sound waves SS12 reflected by an object. The receiving unit 240 includes a receiving element 241, a receiving element 242, and a receiving element 243.

[0049] The signal processing unit 250 causes the transmitting element 230 to transmit a sound wave SS12, receives a receiving signal SR21 corresponding to the sound waves RS14 to RS16 from the receiving element 241, receives a receiving signal SR22 corresponding to the sound waves RS14 to RS16 from the receiving element 242, and receives a receiving signal SR23 corresponding to the sound waves RS14 to RS16 from the receiving element 243.

[0050] With the above configuration, it is possible to identify the positions of objects in two three-dimensional regions, one at a time.

[0051] In the HMD 300, two different positions P1 and P2 are shown, for example, the front (position P1) and the side (position P2) of the display. A first position detection unit TR1 is disposed at position P1, and a second position detection unit TR2 is disposed at position P2.

[0052] Since the transmitting and receiving elements are located on the sides of the HMD, the position of the hand on the side of the HMD can also be detected, making it possible to detect the hand position over a wider range.

[0053] (Variant 1) In embodiment 3, in a configuration in which a transmitter / receiver is arranged on each of the front (position P1) and side (position P2) of the HMD, the frequency of the sound waves transmitted by the transmitting element 210 arranged on the front and the frequency of the sound waves transmitted by the transmitting element 230 arranged on the side are different frequencies.

[0054] If the frequencies were the same, the reflected waves from both hands would be detected by the receiving elements on both the front and sides, making accurate measurements impossible. By changing the frequencies of the transmitting elements placed on the front and sides, it is possible to use a bandpass filter or similar to set different frequencies to be detected among the sound waves received by the receiving elements. Therefore, even if both hands are brought close to the front and sides at the same time, it is possible to detect their positions independently.

[0055] For example, in the case of two transmitting elements spaced about 20 kHz apart, 50 kHz or 70 kHz (or even 90 kHz for three elements) can be used. The extent to which the frequencies of the transmitting elements are separated must be determined based on the element characteristics, primarily the Q value. In this case, it is necessary to specify that the frequency of the sound waves used by one transmitting element is sufficiently separated from the resonant frequency of the other transmitting element.

[0056] (Variant 2) In embodiment 3, in a configuration in which a transmitter / receiver is arranged on each of the front (position P1) and side (position P2) of the HMD, even if the frequency of the sound waves transmitted by the transmitting element 210 arranged on the front and the frequency of the sound waves transmitted by the transmitting element 230 arranged on the side are the same, similar detection is possible by shifting the transmission timing.

[0057] For example, even if the same frequency is used, transmission and reception of the transmitting element 210 and the receiving elements 221 to 223 in the position detection unit TR1 can be alternated with transmission and reception of the transmitting element 210 and the receiving elements 221 to 223 in the position detection unit TR1, but in this case the frame rate will be reduced to half or less.

[0058] Embodiment 4. In the HMD of embodiment 3 in which position detection units TR1 and TR2 are disposed on the front and side, the position of the pointer on the screen is controlled based on the position of the hand detected on the front, and the action of the pointer on the screen is controlled based on the position of the other hand detected on the side. Note that it is also possible to control the position of the pointer on the screen based on the position of the hand detected on the side, and control the action of the pointer on the screen based on the position of the other hand detected on the front.

[0059] The actions are actions typically performed with a mouse, such as selecting or dragging. Actions are assigned in correspondence with hand movements, such as moving your hand close to the HMD and then moving it away, or moving your hand in a circular motion. This allows for more complex control of the HMD using hand movements.

[0060] Generally, the pointer position and actions of an HMD are realized by wearing an inertial force sensor on the hand or by pressing a button held in the hand, but in this embodiment, it is not necessary to wear a sensor on the hand.

[0061] (Summary) Hereinafter, the embodiment will be summarized with reference to the drawings again.

[0062] (1) The present disclosure relates to a measurement system. The measurement system 1 shown in Fig. 1 includes a first transmitting element 10 that generates a first sound wave SS1 to be transmitted, a first receiving element 20 that receives second sound waves RS1 to RS3 that are reflected from an object from the first sound wave SS1, and a signal processing unit 30 that causes the first transmitting element 10 to transmit the first sound wave SS1 and receives a first received signal SR1 corresponding to the second sound waves RS1 to RS3 from the first receiving element 20. As shown in Figs. 3 and 4 , the signal processing unit 30 is configured to calculate the distance to the object based on the latest time tf at which the amplitude of the first received signal SR1 exceeds a threshold value St within a certain time tm from the time ts when the first sound wave SS1 is emitted.

[0063] (2) The measurement system described in paragraph 1 further includes a second receiving element 122 that is disposed at a different position from the first receiving element 121 and receives a second sound wave, as in the measurement system 101 shown in Figures 6 and 9. The signal processing unit 130 receives a second receiving signal SR2 corresponding to the second sound wave from the second receiving element 122, and detects the position of the object based on the first receiving signal SR1 and the second receiving signal SR2.

[0064] (3) The measurement system described in paragraph 2, like the measurement system 201 shown in Figures 10 and 11, further includes a second transmission element 230, a third reception element 241, and a fourth reception element 242 in addition to a first transmission element 210 that generates a first sound wave SS1 to be transmitted and a first reception element 221 and a second reception element 222 that receive second sound waves RS1 to RS3 that are generated when the first sound wave SS1 is reflected by an object. The second transmission element 230 is located at a different position from the first transmission element 210 and generates a third sound wave SS12 to be transmitted. The third reception element 241 is located at a different position from the first reception element 221 and the second reception element 222 and receives a fourth sound wave that is generated when the third sound wave SS12 is reflected by an object. The fourth reception element 242 is located at a different position from the first reception element 221, the second reception element 222, and the third reception element 241 and receives the third sound wave. The signal processing unit 250 causes the second transmitting element 230 to transmit a third sound wave SS12, receives a third received signal SR21 corresponding to the fourth sound wave from the third receiving element 241, and receives a fourth received signal SR22 corresponding to the fourth sound wave from the fourth receiving element 242. The signal processing unit 250 is configured to detect the position of the object based on the first to fourth received signals SR11, SR12, SR21, and SR22.

[0065] (4) In the measurement system described in paragraph 3, the first sound wave SS11 and the third sound wave SS12 have different frequencies.

[0066] (5) In the measurement system described in paragraph 3, the first sound wave SS11 and the third sound wave SS12 have different transmission times (emission times, radiation times).

[0067] (6) In the measurement system described in paragraph 3, as shown in Figures 10 and 12, the first transmitting element 210, the first receiving element 221, and the second receiving element 222 constitute a first position detection unit TR1, and the second transmitting element 230, the third receiving element 241, and the fourth receiving element 242 constitute a second position detection unit TR2. The target object includes both hands, and the signal processing unit 250 is configured to recognize the position of a first hand of both hands detected by the first position detection unit TR1 as the position of the pointer, and to recognize the position of a second hand of both hands detected by the second position detection unit TR2 as a position indicating an action.

[0068] (7) In another aspect, the present disclosure relates to a head-mounted display including the measurement system according to any one of (1) to (6).

[0069] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0070] 1, 101, 201 Measurement system, 2, 10, 110, 210, 230 Transmitting element, 20, 121-123, 221-223, 241-243 Receiving element, 30, 130, 250 Signal processing unit, 120, 220, 240 Receiving unit, J1, J2, J3 Object, TR1, TR2 Position detection unit.

Claims

1. a first transmitting element that generates a first acoustic wave for transmission; a first receiving element that receives a second sound wave that is the first sound wave reflected by an object; a signal processing unit that causes the first transmitting element to transmit the first sound wave and receives a first received signal corresponding to the second sound wave from the first receiving element, The signal processing unit is configured to calculate the distance to the object based on the reception time of the second sound wave, of which the amplitude of the first received signal exceeds a judgment value, that is received latest from the time the first sound wave is emitted.

2. The signal processing unit has a maximum distance measurement time that is predetermined based on a maximum distance to the object, The measurement system of claim 1, wherein the signal processing unit is configured to calculate the distance to the object based on the latest time at which the amplitude of the first received signal exceeds a judgment value within the maximum distance measurement time from the time the first sound wave is emitted.

3. Further, a second receiving element is disposed at a position different from the first receiving element and receives the second sound wave, The measurement system according to claim 1 , wherein the signal processing unit receives a second reception signal corresponding to the second sound wave from the second reception element and detects the position of the object based on the first reception signal and the second reception signal.

4. a second transmitting element disposed at a position different from the first transmitting element and generating a third acoustic wave for transmission; a third receiving element disposed at a position different from the first receiving element and the second receiving element, and configured to receive a fourth sound wave resulting from the third sound wave being reflected by an object; a fourth receiving element disposed at a position different from the first receiving element, the second receiving element, and the third receiving element, and configured to receive the third sound wave; The signal processing unit causes the second transmitting element to transmit the third sound wave, receives a third received signal corresponding to the fourth sound wave from the third receiving element, and receives a fourth received signal corresponding to the fourth sound wave from the fourth receiving element; The measurement system according to claim 3 , wherein the signal processing unit is configured to detect a position of the object based on the first to fourth received signals.

5. The measurement system of claim 4 , wherein the first sound wave and the third sound wave have different frequencies.

6. The measurement system according to claim 4 , wherein the first sound wave and the third sound wave are transmitted at different times.

7. the first transmitting element, the first receiving element, and the second receiving element constitute a first position detection unit, the second transmitting element, the third receiving element, and the fourth receiving element constitute a second position detection unit, the object includes both hands, 5. The measurement system of claim 4, wherein the signal processing unit is configured to recognize the position of a first hand of both hands detected by the first position detection unit as the position of a pointer, and to recognize the position of a second hand of both hands detected by the second position detection unit as the position indicating an action.

8. A head-mounted display comprising the measurement system according to any one of claims 1 to 7.