HEAD-MOUNTED DEVICE FOR REDUCING SYMPTOMS OF CYBERSICKNESS

A head-mounted device for reducing symptoms of cybersickness includes a main shell, and a stimulation unit. The main shell includes first, second and third tube bodies that are arc-shaped and that are worn respectively on the top and back of the user’s head and the user’s ear. The stimulation unit includes first, second and third components that are received respectively in the first, second and third tube bodies, that are movable in a rolling, sliding or flowing manner with low friction, and that are configured to generate and transmit a stimulation force, through one end of the respective one of the first, second and third tube bodies, to the use’s vestibular system in respond to movement of the user’s head.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese Patent Application No. 111109557, filed on Mar. 16, 2022.

FIELD

The disclosure relates to a head-mounted device, and more particularly to a head-mounted device for reducing symptoms of cybersickness.

BACKGROUND

With the rising popularity of virtual reality (VR) or augmented reality (AR) head-mounted displays, an increasing number of users have reported experiencing cybersickness, which is a form of motion sickness occurring as a result of exposure to VR or AR environments. Specifically, cybersickness is presumed to occur when a user’s perception of self-motion based on visual inputs from a VR or AR device is at odds with that based on sensory inputs from the user’s vestibular system (i.e., when what is perceived visually does not match with what is perceived by the vestibular system). As a result, symptoms such as pallor, headache, and dizziness, are often induced.

In order to reduce the symptoms of cybersickness, an existing method proposed to reduce the above-mentioned visual-vestibular conflicts by changing the displayed content of the head-mounted display. However, such method can detract from the intended VR or AR effect of the head-mounted display, thus lowering its value in the entertainment industry or affecting its ability in delivering information with precision in the medical or educational field.

In addition, an existing control system with the same objective proposed to control a motor based on movement of the user’s head, so that the motor drives a stimulating object (e.g., a tapping object) to stimulate the user’s vestibular system. However, since such control system needs to perform system calculations before transmitting signals to the motor, a time delay is perceivable by the user which can compromise the stimulation effect of the system in reducing the visual-vestibular conflicts.

SUMMARY

Therefore, the object of the disclosure is to provide a head-mounted device that can alleviate at least one of the drawbacks of the prior art.

According to the disclosure, the head-mounted device for reducing symptoms of cybersickness is adapted to be worn on a user’s head and to be used cooperatively with a head-mounted display. The head-mounted device includes a main shell and a stimulation unit.

The main shell is adapted to be mounted on the user’s head, and includes a first tube body, a second tube body and a third tube body that are adapted to be respectively disposed at the top of the user’s head, the back of the user’s head and one of the user’s ears. The first, second and third tube bodies are arc-shaped, have arc-shaped central axes which respectively define imaginary first, second and third planes, and are fixedly connected to one another in a manner that the first, second and third planes are perpendicular to one another. Each of the first, second and third tube bodies has opposite closed ends. For each of the first and second tube bodies, each of the closed ends is adapted to be disposed proximal to a respective one of the user’s ears.

The stimulation unit includes a first component, a second component and a third component. Each of the first, second and third components is received in a respective one of the first, second and third tube bodies, and is configured to be movable in at least one of rolling, sliding and flowing manners with low friction in the respective one of the first, second and third tube bodies.

When rotation of the user’s head drives at least one of the first, second and third components of the stimulation unit to move in the respective one of the first, second and third tube bodies, the at least one of the first, second and third components is adapted to generate and transmit a stimulation force, through one of the closed ends of the respective one of the first, second and third tube bodies, to the user’s vestibular system for stimulating the user’s vestibular perception.

When the at least one of the first, second and third components is composed of at least one rigid body, the stimulation force is proportional to an angular acceleration of the user’s head, a total mass of the at least one rigid body, and a radius of curvature of the respective one of the first, second and third tube bodies.

When the at least one of the first, second and third components is composed of a fluid, the stimulation force is proportional to the angular acceleration of the user’s head, the radius of curvature of the respective one of the first, second and third tube bodies, an inner cross-sectional area of the respective one of the first, second and third tube bodies, and a density of the fluid.

DETAILED DESCRIPTION

Referring toFIGS.2to4, a head-mounted device100for reducing symptoms of cybersickness according to the disclosure is adapted to be worn on a user’s head and to be used cooperatively with a VR or AR head-mounted display (not shown). When in use, the head-mounted device100counteracts visual-vestibular conflicts induced by the head-mounted display by applying physical stimulation to the user’s vestibular system in response to motions of the user’s head (e.g., tilting, turning, nodding, or a combination thereof) to stimulate the user’s vestibular perception, thereby reducing symptoms of cybersickness. The head-mounted device100includes a main shell1and a stimulation unit.

Referring toFIG.8, for the purpose of explanation, three principle anatomical planes of the user’s body (i.e., coronal, sagittal, and horizontal planes) are defined hereafter in reference to a coordinate system having X-, Y- and Z-axes. Specifically, the coronal plane that divides the user’s head into front and rear portions is defined by an Y-Z plane of the coordinate system. The sagittal plane that divides the user’s head into left and right portions is defined by an X-Z plane of the coordinate system. The horizontal plane that that is perpendicular to the coronal and sagittal planes and that is disposed at same level as the user’s neck is defined by an X-Y plane of the coordinate system.

In the present embodiment, movement of the user’s head includes at least one of the following: roll movement (i.e., a head tilt towards either of the shoulders) about a first axis (not shown) parallel to the X-axis; yaw movement (i.e., a side-to-side head rotation) about a second axis (not shown) parallel to the Z-axis; and pitch movement (i.e., a downward or upward head tilt) about a third axis (not shown) parallel to the Y-axis.

The configurations and operation of the head-mounted device100are described hereinafter in reference to when the head-mounted device100is worn on the user’s head.

The main shell1is adapted to be mounted on the user’s head with aid of a fastening strap (not shown), and includes an arc-shaped first tube body11, an arc-shaped second tube body12and two arc-shaped third tube bodies13. In the present embodiment, each of the first, second and third tube bodies11,12,13is semicircular and provided with a circular inner cross-section, but is not limited thereto in variations of the embodiment.

As shown inFIG.2, the first tube body11is adapted to be disposed at the top of the user’s head. The second tube body12is adapted to be disposed at the back of the user’s head. The third tube bodies13are adapted to be disposed at the user’s ears, respectively. Each of the first, second and third tube bodies11,12,13has opposite closed ends. For each of the first and second tube bodies11,12, each of the closed ends is adapted to be disposed proximal to a respective one of the user’s ears. For each of the third tube bodies13, one of the closed ends is connected to a respective one of the closed ends of the first tube body11.

The main shell1further includes two first fixing members14that are connected between the first and second tube bodies11,12, and two second fixing members15that are connected between the second and third tube bodies12,13. Specifically, each of the first fixing members14has one end connected to a respective one of the close ends of the first tube body11, and an opposite end connected to a respective one of the close ends of the second tube body12. Each of the second fixing members15has one end connected to one of the close ends of a respective one of the third tube bodies13, and an opposite end connected to a segment of the second tube body12proximal to a respective close end of the second tube body12.

The first and second tube bodies11,12have arc-shaped central axes that respectively define imaginary first and second planes. The third tube bodies13have arc-shaped central axes that respectively define imaginary third and fourth planes which are parallel to each other. The first, second and third tube bodies11,12,13are fixedly connected to one another by the first and second fixing members14,15in a manner that the first and second planes are perpendicular to each other and to the third and fourth planes.

It should be noted that, referring toFIG.3in conjunction withFIG.8, the first plane is parallel to the coronal plane (or may be coplanar with the coronal plane in variations of the embodiment). The second plane is parallel to the horizontal plane. The third and fourth planes are parallel to the sagittal plane.

It should also be noted that a radius of curvature of each of the first, second and third tube bodies11,12,13is determined based on a database of two-dimensional head sizes of users.

In variations of the embodiment, the main shell1may include only one third tube body13, one first fixing member14and one second fixing member15. In addition, in these variations, each of the first, second and third tube bodies11,12,13may has a semicircular or U-shaped inner cross section.

Referring again toFIGS.2and3, in the present embodiment, the stimulation unit includes a first component2, a second component3and two third components4. Each of the first and second components2,3is movably received in a respective one of the first and second tube bodies11,12. Each of the third components4is movably received in a respective one of the third tube bodies13. In variations of the embodiment, in which the main shell1includes only one third tube body13, the stimulation unit may include only one third component4.

Specifically in the present embodiment, each of the first, second and third components2,3,4is configured to be movable in at least one of rolling, sliding and flowing manners with low friction in the respective one of the first, second and third tube bodies11,12,13.

When the user’s head rotates while watching images of the head-mounted display, rotation of the user’s head drives at least one of the first, second and third components2,3,4of the stimulation unit to move in the respective one of the first, second and third tube bodies11,12,13, and the at least one of the first, second and third components2,3,4is adapted to generate and transmit a stimulation force, through one of the closed ends of the respective one of the first, second and third tube bodies11,12,13, to the user’s vestibular system for stimulating the user’s vestibular perception.

Before an operation of the head-mounted device100is described in detail hereafter, please refer toFIG.1, which illustrates the physical principle of motion to which operation of the head-mounted device100accords. Specifically,FIG.1illustrates momentum transferring among an elongated closed tube that has a circular cross-section, and a plurality of steel balls (whose total mass is designated by m) that are disposed in the closed tube. The momentum transferring process is divided into three stages: a first stage, a second stage and a third stage.

In the first stage, when a right end of the closed tube is subjected to an external force Fs, the closed tube and the steel balls move together toward the left at an acceleration αs. In this case, according to Newton’s second law of motion, the steel balls gain a momentum during the movement, and exerts an equal amount of reaction force Fson the closed tube, wherein Fs= m × αs.

In the second stage, after the external force is removed and the closed tube stops moving, the momentum of the steel balls drives the steel balls to continue moving toward the left at a constant velocity Vs(it should be noted that, in this case, a friction force is nearly negligible so that rolling resistance is ignored). Given the steel balls are driven by the closed tube over a duration of time t1, an impulse of the steel balls is Fs× t1= m × ΔV, wherein m × ΔV is a change in the momentum of the steel balls, and ΔV is a change in the velocity of the steel balls relative to the closed tube from the time the steel balls start to move with the closed tube (i.e., relative velocity is zero) to the time they move relative to the closed tube at the constant velocity VS, and the momentum of the steel balls is m × VS.

Finally, in the third stage, the steel balls hit a left end of the closed tube and transfer their momentum to the closed tube until they no longer move relative to the closed tube. In this case, given a duration of time that the steel balls hit the closed tube until fully stopped (i.e., the velocity of the steel balls changes from Vsto 0) is t2, and a change in the velocity of the steel balls is ΔV=(Vs-0)=Vs, a change in the momentum of the steel balls (i.e., m×Vs) is equal to an impulse of the steel balls applied to the closed tube, that is, m×Vs=FB×t2, where FBis a force exerted by the steel balls on the closed tube. As such, the force of the steel balls can be obtained as

In view of the above, when each of the first, second and third components2,3,4is composed of at least one rigid body (i.e., the steel balls shown inFIG.3, but not limited thereto in variations of the embodiment), the stimulation force is proportional to an angular acceleration of the user’s head, a total mass of the at least one rigid body, and a radius of curvature of the respective one of the first, second and third tube bodies11,12,13.

In addition, the above-mentioned physical principle of motion can be applied to any of the following combinations: a combination of the first tube body11and the first component2; a combination of the second tube body12and the second component3; and a combination of each of the third tube bodies13and the respective one of the third components4. Application of the motion principle for each of the afore-mentioned combinations is described in detail hereinafter with reference toFIGS.5to7.

Referring toFIG.5, when the user’s head tilts toward the right side of the drawing (i.e., toward the user’s left shoulder), it rotates about the first axis (in a clockwise direction as shown in the drawing). Given an angular acceleration of rotation is αh1, a tangential acceleration αs1, in an upward tangential direction of the first tube body11is generated by the angular acceleration αh1, and is obtained as αs1, = R1×αh1, wherein R1is a radius of curvature of the first tube body11. Therefore, according to Newton’s second law of motion, the stimulation force applied by the first component2to the user’s vestibular system can be obtained as F1= m1×R1× αh1, wherein m1is a mass of the first component2.

Similarly, referring toFIG.6, when the user’s head rotates toward the right about the first axis (in a clockwise direction as shown in the drawing). Given an angular acceleration of rotation is αh2, a tangential acceleration αs2in a rearward tangential direction of the second tube body12is generated by the angular acceleration αh2, and is obtained as αs2= R2×αh2, wherein R2is a radius of curvature of the second tube body12. Therefore, according to Newton’s second law of motion, the stimulation force applied by the second component3to the user’s vestibular system can be obtained as F2= m2× R2× αh2, wherein m2is a mass of the second component3.

Similarly, referring toFIG.7, when the user’s head tilts backwards, it rotates about the third axis (in a clockwise direction as shown in the drawing). Given an angular acceleration of rotation is αh3, a tangential acceleration αs3in an upward tangential direction of each of the third tube bodies13(only one is shown) is generated by the angular acceleration αh3, and is obtained as αs3= R3× αh3, wherein R3is a radius of curvature of the third tube bodies13. Therefore, according to Newton’s second law of motion, the stimulation force applied by each of the third components4(only one is shown) to the user’s vestibular system can be obtained as F3= m3× R3× αh3, wherein m3is a mass of each of the third components4.

Therefore, the head-mounted device100can be designed based on the above results to generate effective stimulation forces.

Further, referring toFIG.9, in a variation of the embodiment, when each of the first, second and third components2,3,4is composed of a fluid, the stimulation force is proportional to the angular acceleration of the user’s head, the radius of curvature of the respective one of the first, second and third tube bodies11,12,13, an inner cross-sectional area of the respective one of the first, second and third tube bodies11,12,13, and a density of the fluid.

In this case, Newton’s second law of motion can be applied in conjunction with Bernoulli’s principle with the following equation:

wherein p is the density of the fluid. Specifically, referring again toFIG.1, assuming the fluid in the closed tube is pushed by the closed tube in the first stage and generates the impulsive force in the second stage, and assuming a fluid pressure applied to the right end of the closed tube in the second stage is P1=0 with a flow velocity of υ1=V, and a fluid pressure applied to the left end of the closed tube is P2= P with a flow velocity of υ2=0. Then, since a fluid force applied by the fluid to the closed tube in the third stage can be obtained as

wherein A is an internal cross-sectional area ofthe closed tube and r is an inner radius of the closed tube, the fluid forces corresponding respectively toFIGS.5to7(i.e., F1, F2and F3) can be obtained by the equation

as follow:

wherein r1is an inner radius of the first tube body11, p1is a density of the first component2(i.e., density of fluid in the first tube body11), and V1is a tangential velocity of the first tube body11;F2=12πr22ρ2V22,wherein r2is an inner radius of the second tube body12, ρ2is a density of the second component3(i.e., density of fluid in the second tube body12), and V2is a tangential velocity of the second tube body12; andF3=12πr32ρ3V32,wherein r3is an inner radius of each of the third tube bodies13, ρ3is a density of each of the third components4(i.e., density of fluid in the third tube bodies13), and V3is a tangential velocity of each of the third tube bodies13.

Similarly, as mentioned above, given the effective vestibular stimulation force is 0.225 kg (or 2.205 N), maximum referential angular velocities of human head rotations are 12.6 rad/s (roll movement), 25 rad/s (yaw movement) and 17.4 rad/s (pitch movement), and radii of curvature fitting for the human head are R1=R2=90 mm and R3= 30 mm, a maximum upward tangential velocity of the first tube body11can be obtained as V1= 0.09 × 12.6 = 1.13 m/s, a maximum backward tangential velocity of the second tube body12can be obtained as V2= 0.09 × 25 = 2.25 m/s, and a maximum upward tangential velocity of each of the third tube bodies13can be obtained as V3= 0.03 × 17.4 = 0.52 m/s. In addition, when each of the first, second and third components2,3,4is composed of the same fluid, such as water, with a density of ρ1= ρ1= ρ1= 1000 kg/m3. Then, according to

wherein n = 1,2,3, the minimum inner radii of the first, second and third tube bodies11,12,13can be obtained as r1≈ 10.6 mm, r2≈ 5.3 mm and r3≈ 23 mm, respectively. As such, the head-mounted device100can be designed based on the above results to generate effective stimulation forces.

In summary, by virtue of the configurations of the main shell1and the stimulation unit, when the head-mounted device of the present disclosure is used cooperatively with the head-mounted display, kinetic energy generated by the movement of the user’s head can be converted to a stimulation force and fed back through indirect means to a region of the user’s head disposed near the vestibular system. As such, the stimulation force provides additional sensory stimulation to the user’s vestibular system to counteract the visual-vestibular conflicts, thereby reducing the symptoms of cybersickness. Furthermore, compared with the prior art, the head-mounted device of the present disclosure does not require a control system to perform system calculations, and thus is able to ensure an immediate stimulation effect without any perceivable time delay.