Apparatus for loading vibration

According to one embodiment, an apparatus for loading vibration is provided. The apparatus for loading vibration has a contacting unit, a first vibration unit, a storage unit and a control unit. The contacting unit is capable of coming into contact with a biological body which pulsates or beats in a contact state of a first contact condition. The first vibration unit provides a self-excited vibration to the biological body through the contacting unit. The storage unit stores a second contact condition which synchronizes the self-excited vibration with the pulses or the beats. The control unit controls the contact state of the contacting unit so as to make the first contact condition become closer to the second contact condition.

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2012-62848, filed on Mar. 19, 2012, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an apparatus for loading vibration.

BACKGROUND

A mechanical behavior of tissues inside a biological body such as a headache, a bedsore or a pulmonary thromboembolism may be a cause of decreasing a biological function inside the biological body. The headache is caused, when a pulse displacement of blood vessels becomes larger than that caused under a nor mal condition and the adjacent nerves are irritated. The bedsore and the pulmonary thromboembolism (an economy class syndrome) are caused when blood flow in the blood vessels is restricted by a continued load.

A technique for preventing such decrease of a biological function caused by a mechanical behavior of tissues inside a biological body is desired.

DETAILED DESCRIPTION

In the following description, “vibration” indicates a movement including “oscillation”.

According to one embodiment, an apparatus for loading vibration is provided. The apparatus for loading vibration has a contacting unit, a first vibration unit, a storage unit and a control unit. The contacting unit is capable of coming into contact with a biological body which pulsates or beats in a contact state of a first contact condition. The first vibration unit provides a self-excited vibration to the biological body through the contacting unit. The storage unit stores a second contact condition which synchronizes the self-excited vibration with the pulses or the beats. The control unit controls the contact state of the contacting unit so as to make the first contact condition become closer to the second contact condition.

Hereinafter, further embodiments will be described with reference to the drawings.

In the drawings, the same reference numerals denote the same or similar portions respectively.

Apparatuses for loading vibration according to the embodiments are configured to adjust pulses or beats by using an entrainment (synchronization) described below. The entrainment is generated by providing self-excited vibration to circulatory systems such including ductus arteriosus, ductus venosus, capillary blood vessels (hereinafter collectively referred to as “blood vessels”) or lymph vessels which pulsate inside a biological body, or to internal organs such as a heart which beat.

A description described below is made with reference to an example of adjusting pulses of the blood vessels.

When a non-linear phenomenon according to a natural system or a non-natural system, for example, behaviors of a group of self-excited vibrators which interact, or self-excited vibration (limit cycle vibration) in a forcible vibration system satisfies a condition, a phenomenon where frequencies or phases of the vibration synchronize occurs.

A phenomenon where a rhythm of a non-linear vibrator is dragged to another stable rhythm and the former rhythm is synchronized with the stable rhythm is referred to as “entrainment (synchronization)”.

The drawing phenomenon includes a frequency entrainment (frequency locking) and a phase entrainment (phase locking). In the frequency entrainment, frequencies are synchronized. In the phase entrainment, not only frequencies but also phases are synchronized. In a case where the frequency of a cyclic forced vibration is ω, and the frequency of the self-vibration is Ω, the following equation is satisfied when a frequency entrainment arises. In the following equation, n and m are integers equal to or greater than one which may be arbitrarily determined in advance.
n·ω=m·Ω(1)

Further, in a case where the phase of the forced vibration is ϕ1, and the phase of the self-excited vibration is ϕ2, the following equation is satisfied when a phase entrainment arises. In the following equation, the constant X is π/4, for example. The phase locking is performed within a scope which meets the following equation.
|n·ϕ1−m·ϕ2|<X(2)

The following description will be made with regard to an example of performing a frequency locking in a case where the integer n=1, the integer m=1, and the phase difference between the forced vibration and the self-excited vibration is 0 (in phase) or π (in reverse phase).

Two kinds of entrainments may occur, and they are an entrainment in phase and an entrainment in reverse phase, as illustrated inFIGS. 1A and 1B.FIG. 1Ais a diagram illustrating the entrainment in phase, andFIG. 1Bis a diagram illustrating the entrainment in reverse phase.

In the case of the entrainment occurring in phase as illustrated inFIG. 1A, the self-excited vibration and the forced vibration induce entrainment so that the phases match and the frequencies synchronize as time passes. At this time, the amplitude of the forced vibration becomes large.

On the other hand, in the case of the entrainment occurring in reverse phase as illustrated inFIG. 1B, the self-excited vibration and the forced vibration induce entrainment so that the phases deviate by π and the frequencies synchronize as time passes. At this time, the amplitude of the forced vibration becomes small.

The following description will be made with regard to a configuration example of a mechanism for loading self-excited vibration which generates a self-excited vibration.

In order to describe a configuration example of the mechanism for loading self-excited vibration, a case where a flutter and a galloping caused by a flowable medium flows around a square cylinder will be explained as an example. The movement of the square cylinder is limited by springs and dashpots so that the square cylinder moves in a direction perpendicular to a flow of the medium.

As to the mechanism for loading self-excited vibration, the mechanical behavior of the square cylinder which provides loads to body tissues may be expressed by the following equation.
mÿ+r{dot over (y)}+ky=F({dot over (y)})  (3)

In the following equation, y represents a displacement of the square cylinder. m represents mass of the square cylinder, r represents a viscosity coefficient which shows a dumping in the mechanical behavior of the square cylinder. k represents an elastic coefficient in the mechanical behavior of the square cylinder. In addition, F in the right-hand side represents a driving force for inducing self-excited vibration to the square cylinder.

When the velocity of the square cylinder is V1and the flow velocity of the medium is V2, the relative velocity of the medium with respect to the square cylinder is represented by (V12+V22)1/2. The relative velocity provides the vertical force to the square cylinder as a fluid force. The fluid force is represented by a function of an angle formed by a relative speed and a flow direction of the medium.

At this time, the driving force may approach to the following function form (equation). In the following equation, ρ represents a density of the medium. V represents a flow velocity of the medium. “a” represents an area of a front surface (seen in the flow direction of the medium) of the square cylinder. C represents a fluid force.

When the form of the square cylinder and the density of the medium are appropriately selected, A3=0 and A4=0 are satisfied. As a result, the driving force of the mechanism which performs the self-excited vibration may be expressed in the form of C1(=the velocity of the square cylinder)−C2(=(the velocity of the square cylinder)3), in the example. Accordingly, the equation 3 may be substituted to the following equation.
mÿ+r{dot over (y)}+ky=C1({dot over (y)})−C1({dot over (y)})3(5)

Both of the sides of the equation 5 are differentiated with respect to time, and the velocity of the square cylinder is replaces with a new variable y. The above equation with respect to y is represented by a Van Der Pol equation shown as the following equation. In the following equation, α is a load parameter relating to the vibration of the mechanism for loading self-excited vibration.
ÿ−α(1−y2){dot over (y)}+y=0  (6)

when the forced vibration provided on the self-excited vibration is represented by a periodic function ε sin(ωt), for example, the interaction between the self-excited vibration and the forced vibration is represented by the following equation. In the following equation, ε is an interaction parameter which represents the intensity of the interaction between the forced vibration and the self-excited vibration.
ÿ−α(1−y2){dot over (y)}+y=εsin(ωt)  (7)

The load parameter α and the interaction parameter ε which influence the induction of the entrainment will be described below.

The load parameter α is a parameter relating to the vibration of the mechanism for loading self-excited vibration, and may include the amplitude and the frequency of the vibration generation source (for example, a flutter, a galloping or a piezo-actuator based on vibration) which induces the vibration in the mechanism for loading self-excited vibration.

The interaction parameter ε is a parameter which represents a condition for contacting the body, the characteristics of materials (including the skin of the body) which are interposed between the body tissues and the mechanism for loading self-excited vibration and so on. The parameter may include load-deformation characteristics which the materials have, thicknesses of the materials, and the contact pressure of the mechanism to the body when the mechanism is fixed on the body.

When the solution of Equation 7 is described as y=A(t)sin(ωt+ϕ(t)), the difference Δω between the frequency of the self-excited vibrator and the frequency of the forced vibration is required to satisfy the following equation in order to cause an entrainment.
−ε/(2A)<Δω<ε/(2A)  (8)

The entrainment may be induced by adjusting the load parameter α and the interaction parameter ε which adjusts the intensity of the forced vibration, so as to satisfy the above condition.

At this time, in a case where the interaction parameter ε>0, the self-excited vibration and the forced vibration synchronize in reverse phase (the phase deviates by π). Further, in a case where the interaction parameter ε<0, the self-excited vibration and the forced vibration synchronize in phase when the absolute value of ε is sufficiently smaller than the amplitude of the self-excited vibration, and the self-excited vibration and the forced vibration synchronize in reverse phase when the absolute value of ε is sufficiently larger than the amplitude of the self-excited vibration.

Hereinafter, an apparatus for loading vibration according to a first embodiment will be a described. In the embodiment, the apparatus for loading vibration is applied to a health care apparatus such as a cuff which may be wound around the neck, four limbs, or the trunk of a biological body.

FIG. 2is a configuration diagram illustrating the apparatus for loading vibration according to the first embodiment. An apparatus100for loading vibration illustrated inFIG. 2is provided with a measuring unit10as a first measuring unit, a loading unit20as a first vibration unit, a measuring unit30as a second measuring unit, a contacting unit40, a control unit50, and a storage unit60. The measuring unit10measures the pulse rhythm (including the amplitude and the cycle) of the body. The loading unit20provides a self-excited vibration to the body under a first load condition. The measuring unit30measures the amplitude and the cycle of the self-excited vibration. The contacting unit40adjusts a contact state which is a first contact condition between the body and the loading unit20. The control unit50controls an entrainment. The storage unit60stores an initial value of a load condition which is a second load condition and an initial value of a contact condition which is a second contact condition. These units10,20,30,40,50and60are connected to a signal line5.

A computing device such as a CPU or an MPU is used for the measuring unit30and the control unit50. A storage device such as a memory or an HDD is used for the storage unit60.FIGS. 3A and 3Bare schematic diagrams illustrating examples of the apparatus100for loading vibration which are applied to cuffs.

The measuring unit10measures pulse waveforms when the blood vessels pulsate. The pulse waveforms may be the amplitude of the pulse wave and the number or the cycle of the vibration per sampling cycle. For the measuring unit10, a sphygmomanometer or a pulse beat sensor may be used. In a case of using a sphygmomanometer, the sphygmomanometer may be provided in a cuff8which may be wound around the neck, the four limbs, or the trunk of the body7, which has blood vessels6, as illustrated inFIG. 3A or 3B. In a case of using a pulse beat sensor, the pulse beat sensor includes a reference light generating source and a reference light receiving unit which can be attached to the skin surface just above the artery of the body7. The embodiment will be described with regard to the case of using the sphygmomanometer as the measuring unit10.

In general, a blood pressure waveform and a pulse waveform to be obtained by a sphygmomanometer have a relation of almost the same phase, approximately. For the purpose of simplicity, the blood pressure waveform and the pulse waveform are deemed to be a sine wave or a cosine wave. Accordingly, the measuring unit10can measure the amplitude and the cycle of the pulse waveform by measuring the amplitude and the cycle of the blood pressure waveform, indirectly. The measured values of the amplitude and the cycle can be stored in the storage unit60.

The loading unit20is an actuator which loads a self-excited vibration on the body by the contacting unit40. The self-excited vibration may be a self-excited vibration of a Van Der Pol type. The loading unit20performs self-excited vibration by applying command voltage which is calculated by the control unit50. According to the embodiment, the loading unit20is provided in the cuff, and loads the self-excited vibration on the body in such a manner that the cuff is wound around an arm of the body.

Hereinafter, the specific configuration of the loading unit20will be described. A plurality of beams is provided inside the cuff. One ends of the beams are fixed to supporting members and the other ends of beams are free ends. A piezoelectric element is formed at one side of each beam. When a voltage is applied to the piezoelectric element, the piezoelectric element shrinks or stretches so that a flexure of the beam occurs. The distance r from the supporting member of the beam to the leading end is set to 1 (r=1). Hereinafter, the flexure of the beam when the distance r is 1 is referred to as a displacement.

The measuring unit30measures the amplitude and the cycle of the vibration from the loading unit20. The measuring unit30obtains a value of the amplitude from a relation between the displacement and a voltage applied to the piezoelectric element of the loading unit20, for example. Further, the measuring unit30can obtain a value of the cycle of the vibration from the cycle of the applied voltage, which is provided from the control unit50as described below.

The contacting unit40is a member which is provided between the loading unit20and the body and which adjusts the contact state which influences the interaction parameter ε. In the embodiment, the contacting unit40adjusts the contact pressure (pressure force) onto the body by increasing the volume. The increasing of the volume is performed by introducing the air, for example. At this time, the contact state of the contacting unit40is controlled by the control unit50as described below.

The control unit50calculates an input voltage Vc to be supplied to the loading unit20.

According to the self-excited vibration of the Van Der Pol type, the effect of the vibration or the displacement of the loading unit20functions as an acceleration input to the displacement of the cantilever beam. Further, the self-excited vibration has a characteristic that the displacement by the shrinkage or the stretch of an integral type piezoelectric element is nearly proportional to an applied voltage. Accordingly, the control unit50feeds back the linear combination of the integrated value of the displacement of the beam with the cubed integrated value of the displacement of the beam, and calculates the input voltage Vc which is supplied to the loading unit20as shown in the following equation. As an initial condition, predetermined voltage values stored in the storage unit60in advance may be used.
Vc=Klin∫δ|r=1dt−Knon∫δ3|r=1dt(9)

In the above equation, Klin and Knon are a linear feedback gain and a non-linear feedback gain, for example, respectively. In the embodiment, the feedback gains Klin, Knon are values which influence the load parameter α, and the initial values of the feedback gains Klin and Knon are stored in the storage unit60in advance. δ|r=1 is a displacement in a case of r=1 with respect to the loading unit20. As the displacement, an amplitude value obtained from the measuring unit30may be used.

In order to induce synchronization of the biological rhythm and the self-excited vibration of the loading unit20easily, it is desirable that the feedback gains Klin, Knon be set such that the frequency of the self-excited vibration is a value close to the frequency of the biological rhythm, for example, within ±10%.

The control unit50obtains the cycle value of the biological rhythm measured by the measuring unit10and the cycle value of the self-excited vibration measured by the measuring unit30. The obtained cycle values are converted to the frequencies, respectively. When a ratio (hereinafter referred to as “error”) of a deviation of the frequency of the self-excited vibration from the frequency of the biological rhythm to the latter frequency is not within the range of ±10%, the feedback gains Klin and Knon are changed so as to make the frequency of the self-excited vibration become closer to the frequency of the biological rhythm.

When a measurement error arises in measuring the biological rhythm, a variation distribution of the frequency is measured, and the feedback gains Klin, Knon are changed so as to become closer to the average value of the variation distribution of the frequency.

Further, the control unit50controls the operation of the contacting unit40so that the biological rhythm and the self-excited vibration of the loading unit20are synchronized. By the control, the control unit50changes the contact state in which the loading unit20contacts the body.

When the biological rhythm and the self-excited vibration of the loading unit20are synchronized in phase, the amplitude of the biological rhythm (forced vibration) increases with time as illustrated inFIG. 1A. In addition, in s case of synchronization in reverse phase, the amplitude of the biological rhythm decreases with time as illustrated inFIG. 1B.

The control unit50calculates the amplitude difference of the pulse waveform per sampling cycle by using the amplitude of the pulse waveform (blood pressure waveform) measured by the measuring unit10.

For example, when a user selects to synchronize the biological rhythm and the self-excited vibration of the loading unit20in phase by a controller (not illustrated inFIG. 2), the control unit50controls the contacting unit40so as to increase the amplitude of the pulse waveform more to change the contact pressure on the body or to change the load condition of the loading unit20. When the user selects to synchronize the biological rhythm and the self-excited vibration of the loading unit20in reverse phase, the control unit50controls the contacting unit40so as to decrease the amplitude of the pulse waveform more to change the contact pressure on the body or to change the load condition of the loading unit20.

The control unit50compares the amplitude difference of the pulse waveform with a threshold value stored in the storage unit60in advance. When the amplitude is equal to or less than the threshold value, the control unit50determines that the biological rhythm and the self-excited vibration of the loading unit20are synchronized. After the determination, the control unit50controls the contact pressure of the contacting unit40such that the contact pressure is constant.

The storage unit60stores the initial values of the load condition and the contact condition. As the initial values, values which synchronize the biological rhythm with the self-excited vibration may be obtained by simulations or experiments in advance and stored in the storage unit60.

A distribution relating to substance deformation characteristics such as stress, twist and deformation of blood vessel walls and subcutaneous tissues of the body may be prepared in advance. Using the distribution, observation variables such as a response (a displacement and a pressure) from the skin surface of the body, the blood flow waveform and the blood pressure waveform, and the load parameter α (a residual stress, an unstressed state, an external force etc.) and the interaction parameter ε (a pressure etc.) respectively serving as intermediate variables (latent variable) may be identified by a statistical method such as a hierarchical Bayesian model & Markov Chain Monte Carlo method or a particle filter method.

In order to induce the entrainment, a condition in which the load parameter α and the interaction parameter ε are satisfied is obtained from the equations 5, 8. In the embodiment, the relation between the cuff pressure and the load parameter α and the interaction parameter ε which satisfy the equations 5, 8 is obtained by experiments etc. in advance. The value of the cuff pressure is stored in the storage unit60.

Hereinafter, an operation of the apparatus100for loading vibration will be described with reference to the flowchart illustrated inFIG. 4.

The control unit50illustrated inFIG. 2reads out the initial values of the load condition i.e. the feedback gains Klin, Knon and the initial value of the contact condition i.e. the contact pressure of the contacting unit40from the storage unit60(S101).

The control unit50calculates the input voltage Vc based on the equation 9 and applies the calculated input voltage Vc to the loading unit20. By applying the calculated input voltage Vc, the loading unit20generates self-excited vibration and loads the generated self-excited vibration on the body (S102).

The cycle of the biological rhythm is obtained from the measuring unit10, and the cycle of the self-excited vibration is obtained from the measuring unit30. The values of the cycles are stored in the storage unit60. The control unit50converts the values of the cycles stored in the storage unit60into respective frequencies. Further, it is determined whether or not the error of the frequency of the self-excited vibration with respect to the frequency of the biological rhythm is within ±10% (S103).

When the error of the frequency is not within ±10%, the control unit50changes the load condition so as to make the error of the frequency become within ±10%. In other word, the control unit50changes the load condition so as to make the frequency of the self-excited vibration become closer to the frequency of the biological rhythm (S104). When the difference between the frequencies is within ±10%, the load condition is constantly maintained.

When the error of the frequency is within ±10%, the control unit50obtains the amplitude of the biological rhythm from the storage unit60sequentially, and calculates the variation amount of the amplitude i.e. the amplitude difference (S105). The control unit50determines whether or not the amplitude difference is equal to or less than a predetermined threshold value (S106).

When the i.e. the amplitude difference is not equal to or less than the predetermined threshold value, the control unit50changes the load condition or the contact condition so as to decrease the i.e. the amplitude difference of the biological rhythm more, i.e., so that the biological rhythm and the self-excited vibration are synchronized (S107). When the variation amount of the amplitude i.e. i.e. the amplitude difference is equal to or less than the predetermined threshold value, the contact condition is maintained to become constant.

The apparatus for loading vibration according to the embodiment allows the mechanical behavior inside the body to approach an appropriate range. In addition, the control unit50can induce an entrainment despite the differences of bodies by controlling the contacting unit40so as to make the biological rhythm synchronized with the self-excited vibration of the loading unit20.

As illustrated inFIG. 1, when an entrainment is induced, the phase difference between the self-excited vibration and the biological rhythm (a forced vibration) approaches a constant value, and the variation amount of the phase difference decreases.

The control unit50of the vibration loading apparatus may calculate the variation amount of the phase difference between the pulse waveform and the self-excited vibration per sampling cycle by using the amplitude and the cycle of the pulse waveform (a blood pressure waveform) and the amplitude and the cycle of the self-excited vibration.

When a user selects synchronization in phase by a controller (not illustrated inFIG. 2) etc., the contacting unit40can be controlled so that the amplitude of the pulse waveform increases and so that the variation amount of the phase difference decreases. By the control, the pressure on the body can be changed. When the user selects synchronization in reverse phase, the contacting unit40is controlled so that the amplitude of the pulse waveform decreases and so that the variation amount of the phase difference decreases, and, by the control, the pressure on the body can be changed.

As described above, the entrainment can be induced more accurately by using the variation amount of the phase difference and the variation amount of the amplitude i.e. the amplitude difference.

A second embodiment will be described below. There is a phenomenon where the drawing occurs most easily at optimum noise intensity. The phenomenon is called as a stochastic resonance or a stochastic synchronization. This is a phenomenon where vibrations are synchronized at optimum noise intensity when a noise is added to a non-linear system, or where a cycle or phase is drawn to an average cycle when an appropriate noise external force is added to a group of vibrators which have slightly different vibration cycles or phases.

FIG. 5shows a configuration of an apparatus200for loading vibration according to the second, embodiment. The apparatus200is further provided with a loading unit70as a second vibration unit.

The loading unit70is an actuator which loads a minute vibration (disturbance) on a biological body. For example, the loading unit70is provided in a cuff, and loads a minute vibration by winding the cuff around an arm of the body.

As the loading unit70, a piezo-actuator or an ultrasonic actuator which has a random noise for providing amplitude or an load may be used. In the embodiment, a vibration having amplitude which is equal to or less than one-third of amplitude of self-excited vibration from a loading unit20is defined as the minute vibration. The loading unit70is provided near the loading unit20in order to induce a stochastic resonance phenomenon, desirably.

The above apparatus for loading vibration according to the second embodiment can make the mechanical behavior inside the body approach to an appropriate range. Further, it is possible to induce an entrainment despite differences of biological bodies by using the stochastic resonance phenomenon.

The embodiments described above show the case where the apparatuses for loading vibration are applied to the cuff. The apparatuses may be applied to other healthcare devices.FIGS. 6A and 6Bare diagrams illustrating apparatuses for loading vibration according to modified embodiments respectively.FIG. 6Ais a diagram illustrating an apparatus300for loading vibration applied to a bed, andFIG. 6Bis a diagram illustrating an apparatus300afor loading vibration applied to a sofa.

The apparatus300illustrated inFIG. 6Ahas a loading unit20and a contacting unit40provided inside a mattress301of a bed so that the contacting unit40can contact a body7having blood vessels6. A plurality of loading units and a plurality of contacting units may be provided inside the mattress301along a surface of the mattress301. Further, the loading units20and the contacting units40may be provided movably inside the mattress301. In this case, a technology known in the art may be used for a movement mechanism.

The apparatus300aillustrated inFIG. 6Bhas loading units20and contacting units40provided inside a seating surface and a backrest of a sofa302respectively so that the contacting unit40can contact a body7having blood vessels6. A plurality of loading units and a plurality of contacting units may be provided on each of the seating surface and the backrest. The loading unit20and the contacting units40may be provided movably inside the seating surface and the backrest. Further, an additional loading unit and an additional contacting unit may be provided inside an armrest or a footrest (not illustrated inFIG. 6B).

The apparatuses of the embodiments described above can change the mechanical behavior inside the body.