CN110932597A - Variable frequency vibration method capable of shortening response time and vibration actuator - Google Patents
Variable frequency vibration method capable of shortening response time and vibration actuator Download PDFInfo
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Abstract
The invention relates to a variable frequency vibration method and a vibration actuator capable of shortening response time, wherein the vibration actuator comprises a hollow shaft, a vibration output interface and an annular stator elastic body, the annular stator elastic body is sleeved on the hollow shaft, the vibration output interface is fixedly arranged at the top of the hollow shaft through a screw, the hollow shaft is axially locked on the annular stator elastic body, and meanwhile, the annular stator elastic body generates pre-pressure to abut against the vibration output interface; a friction material is laid on the contact surface of the annular stator elastomer and the vibration output interface; piezoelectric ceramics with partitioned polarization are laid on the end face, far away from the vibration output interface, of the annular stator elastic body; a plastic wear-resistant sleeve is arranged between the stator elastic body and the hollow shaft, and the plastic wear-resistant sleeve is sleeved on the hollow shaft; the invention can make up the problem of slow response time of the traditional motor, and the response time of the vibration actuator designed based on the vibration method is greatly improved.
Description
Technical Field
The invention relates to a variable frequency vibration method capable of shortening response time and a vibration actuator, and belongs to the field of annular ultrasonic motors.
Background
Today, handheld intelligent devices in the market are mainly provided with large-sized and high-ratio touch screens, and device manufacturers are drying out physical keys step by step. In contrast, the application of virtual keys and pressure keys is increasing, and virtual keys have many advantages compared with physical keys, such as: the programming is easy, the form and the position are randomly set, and the humanization of the system operation is improved; the service life of the equipment is prolonged, the mechanical structure of the physical key has the performance reduction and the difficult problems of water resistance and dust resistance along with the use, but the virtual key has the fatal defect: the touch feeling is not provided, and because the virtual keys are all arranged on the touch screen, the user has a sense of unreality when using the touch screen, and if the user does not have certain visual or auditory feedback, the user cannot determine whether the keys are pressed; therefore, engineers adopt vibration as feedback of the virtual keys, and the current vibration tactile feedback has achieved the effect of falseness, for example, a pressure-sensitive touch panel of the latest notebook computer of Apple Inc (Apple Inc) and an independent touch panel product Magic Trackpad 2 are good implementation cases; a traditional touch panel generally adopts a rocker structure, as shown in fig. 1a, the touch panel is fixed through a hinge mechanism, the other end of the touch panel is connected with a touch switch, and the touch switch is triggered by pressing the touch panel, so that a step-like pressing hand feeling and button pressing sound are generated; obviously, this structure cannot be pressed down when the top of the touch panel, i.e. near the fixed end of 1a in the figure, is pressed down, which greatly reduces the user experience; in the figure, 1b is a schematic diagram of a pressure-sensitive touch panel structure manufactured by apple company, which is provided with pressure sensors at four corners of the touch panel, and when a user's pressing force reaches a set threshold, a linear vibration motor fixed below the touch panel is started to output vibration with a certain waveform, so as to simulate the touch feeling of pressing (this is a vibration-like phenomenon in tactile psychology, in short, a series of modulated vibrations are used, and an illusion that there is a motion displacement in the touch panel of the user is provided).
In the above, it is mentioned that the combination of virtual keys and vibration actuator instead of physical keys is the development trend of future intelligent devices, and then, for the existing vibration actuator technology, the first one is a rotary Eccentric Rotor Motor (ERM), which is the most common and classic vibration actuating motor, and in the non-smart phone era mobile phones, such a motor is installed, and is an electromagnetic motor, which drives an eccentric mass block to rotate at high speed through a rotating shaft so as to drive a system to vibrate. The ERM has the advantages that the technology is mature, the cost is low, the excitation frequency range is 90Hz-200Hz, but the defects are obvious, and due to the working principle of the electromagnetic motor, the vibration motor has a slow acceleration process when being started and a deceleration process when being stopped, wherein the acceleration process is about 100ms-200ms, so that the vibration of the vibration motor is not crisp, the waveform distortion degree is high, and the user experience is poor; the second type is a linear vibration motor (LRC), the LRC is popular only in recent years and is installed on various intelligent devices, the LRC is driven by electromagnetic force, but the performance is much better than the ERM, the principle is similar to that of an electromagnetic linear motor, a spring mechanism is added to provide reset force for a rotor, when square wave signals are applied to a rotor coil, the rotor reciprocates under the combined action of the electromagnetic force and spring force to play a role in excitation, and the LRC has the advantages that: the start-stop response time is relatively short and can reach 30 ms; because of using the spring, the energy consumption is lower; the excitation frequency range is 150-200 Hz, and the defects are that the excitation of the vibration motor is still reliable in electromagnetic force, no delay response can be really realized, and the capacity of forming complex waveforms is still limited; the third one is a vibration actuator which directly pushes the mass block to vibrate by adopting the deformation of piezoceramics, the vibration actuator does not rely on electromagnetic force, so the mechanical response time is extremely low and can reach within 5ms, the requirement of real-time feedback is met, the excitation frequency range is 150Hz-300Hz, but the vibration intensity generated on the small handheld equipment is still insufficient due to the limitation of the structural size and the voltage.
Disclosure of Invention
The invention provides a variable-frequency vibration method capable of shortening response time and a vibration actuator, which can solve the problem of slow response time of a traditional motor, and the response time of the vibration actuator designed based on the vibration method is greatly improved.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a variable frequency vibration method capable of shortening response time comprises the following steps:
the first step is as follows: writing a two-phase standing wave formula for synthesizing the traveling wave according to the traveling wave synthesis theory of the existing annular ultrasonic motor, and analyzing the relation between the phase difference of the two-phase standing waves and the operation direction of the synthesized traveling wave;
the second step is that: and analyzing the relation between the forward and backward traveling wave particle motion direction and the waveform position to obtain a time-space partial derivative method as a criterion for judging the traveling wave running direction.
The third step: further respectively solving time and space partial derivatives of the forward and reverse traveling wave formulas to prove the correctness of the second step according to the space-time partial derivative method;
the fourth step: writing a superposition formula of the beat travelling wave according to the principle that the standing wave is superposed into the travelling wave, namely changing the superposition of the two-phase standing wave with the same amplitude and frequency and the phase difference of 90 degrees in space and time into the superposition of the two-phase standing wave with the similar amplitude and frequency, and superposing the two-phase standing wave with the phase difference of 90 degrees in space to obtain the formula of the travelling wave;
the fifth step: analyzing the running rule of the beat traveling wave by adopting a space-time partial derivative method, firstly carrying out amplitude normalization processing on a beat traveling wave formula, reserving the waveform motion direction information of the beat traveling wave, secondly obtaining the running direction change rule of the beat traveling wave by adopting the space-time partial derivative method on the beat traveling wave after the amplitude normalization, and finally obtaining the motion direction change period and the frequency of the stator output driving force of the rotary traveling wave ultrasonic motor under the drive mode of the beat traveling wave.
As a further preferred aspect of the present invention, according to the existing standing wave formula of the ring-shaped ultrasonic motor:
W1(θ,t)＝Asinnθcos2πft (1)
the formula (1) and the formula (2) are superposed to obtain a synthetic traveling wave two-phase standing wave formula
When the two standing waves are time-phase-different
Then, equation (3) becomes the forward traveling wave equation:
W＝sin(nθ-ωt) (4)
when the two standing waves are time-phase-different
Then, the formula (3) is changed into a reverse traveling wave formula
W＝sin(nθ+ωt) (5)；
As a further preferred aspect of the present invention, the forward traveling wave downward slope particle is obtained to move upward and the upward slope particle is obtained to move downward according to the position relationship between the moving direction of the forward and backward traveling wave particle and the waveform where the forward traveling wave particle is located, and the backward traveling wave downward slope particle is obtained to move downward and the upward slope particle is obtained to move upward, so that the moving method of the waveform is determined according to the backward direction of the particle movement and the position of the waveform where the particle is located, that is, when the time partial derivative and the space partial derivative of the traveling wave formula are of different signs, the traveling wave is in the forward direction, and when the time partial derivative and the space partial derivative of the traveling wave formula;
as a further preferred aspect of the present invention, the forward traveling wave equation (4) and the backward traveling wave equation (5) are subjected to partial derivatives to obtain equations (6) to (9):
obviously, the equations (6) and (7) have different signs, and the equations (8) and (9) have the same sign, so that a space-time partial derivative method for judging the traveling wave direction is obtained;
as a further optimization of the invention, two-phase standing wave formulas (10) and (11) of the beat travelling wave are obtained through the obtained forward travelling wave formula and the obtained reverse travelling wave formula,
W1'＝sinnθcos(2πf1t+φ10) (10)
W2'＝cosnθcos(2πf2t+φ20) (11)
linearly superposing two-phase standing wave formulas of the beat traveling wave to obtain a synthetic beat traveling wave formula (12) and enabling 2 pi f1＝ω1、2πf2＝ω2After synthesis, W ═ W is obtained1'+W2' is:
W'＝sinnθcos(2πf1t+φ10)+cosnθcos(2πf2t+φ20) (12)；
as a further preferred aspect of the present invention, the step of performing amplitude normalization processing on the traveling wave equation comprises: at t0Time command: a ═ cos (ω)1t0+φ10)、B＝cos(ω2t0+φ20) Then, then
the first partial derivative in time and space is calculated for equation (14):
in comparison of the formulas (15) and (16), the denominator is positive, and the second half of the molecular formula (15) is completely the same as the numerator of the formula (16), so that the symbol relationship between the formulas is determined by the first half of the numerator of the formula (15), that is, the formula (17)
H＝ω1sin(ω1t+φ10)cos(ω2t+φ20)-ω2cos(ω1t+φ10)sin(ω2t+φ20) (17)
After deformation, obtaining:
wherein Δ ω ═ ω1-ω2The difference between two phase circular frequencies is the working frequency of the ultrasonic motor is generally above 20kHz, so the ultrasonic motor has the advantages of simple structure, low cost and high efficiency
Thus:
H≈ω1sin(Δωt+(φ10-φ20)) (19)
formula (19) is a period of
The sine function of (1), wherein Δ f is the difference between two natural frequencies, the first half cycle is positive, and the second half cycle is negative, so that the variation cycle of the running direction of the beat traveling wave is the reciprocal of the natural frequency difference of the two phases, and one half is positive and the other half is reverse; because the direction of the output driving force of the motor stator is opposite to the direction of the traveling wave, the direction of the output driving force of the stator of the traveling wave motor is finally determined to change in a regular cycle similar to a sine function, and the frequency is the difference between two phases of driving frequencies;
a vibration actuator designed based on the variable frequency vibration method comprises a hollow shaft, a vibration output interface and an annular stator elastic body, wherein the annular stator elastic body is sleeved on the hollow shaft, the vibration output interface is fixedly arranged at the top of the hollow shaft through a screw, the hollow shaft is axially locked to the annular stator elastic body, and meanwhile, the annular stator elastic body generates pre-pressure to abut against the vibration output interface;
a friction material is laid on the contact surface of the annular stator elastomer and the vibration output interface;
piezoelectric ceramics with partitioned polarization are laid on the end face, far away from the vibration output interface, of the annular stator elastic body;
a plastic wear-resistant sleeve is arranged between the stator elastic body and the hollow shaft, and the plastic wear-resistant sleeve is sleeved on the hollow shaft;
as a further preferred aspect of the present invention, the piezoelectric ceramic is divided into two symmetrical parts on the surface, namely, a region a and a region B, and the region a and the region B respectively comprise four ceramic sheets.
Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:
1. the stator of the vibration actuator can be driven to vibrate with controllable output frequency and amplitude by depending on the driving principle of beating traveling waves;
2. the piezoelectric actuator adopted by the invention is driven by friction force, the piezoelectric actuator is switched on when being electrified and stopped when being powered off, and the response time of starting and stopping can be shortened to below 1 millisecond, so that people can not feel delay;
3. the vibration actuator provided by the invention has low response delay and self-locking property, and the waveform distortion degree can be greatly reduced;
4. the vibration actuator is based on the principle of an ultrasonic motor, takes contact friction force as driving force, and has good advantages for the current handheld electronic equipment because the motor is not provided with an electromagnetic coil and does not generate a magnetic field;
5. the vibration actuator designed based on the variable frequency vibration method has various forms and flexible design.
Drawings
The invention is further illustrated with reference to the following figures and examples.
Fig. 1 is a schematic diagram of a conventional touch panel and a structure of a pressure-sensitive touch panel of apple, wherein 1a is a schematic diagram of a conventional touch panel structure, and 1b is a schematic diagram of a structure of a hole plate of a pressure-sensitive touch panel of apple;
FIG. 2 is a schematic diagram of the forward traveling wave of the preferred embodiment of the present invention (dt → 0);
FIG. 3 is a schematic reverse traveling wave diagram (dt → 0) of a preferred embodiment of the present invention;
FIG. 4 is a time-varying deployment diagram of a traveling beat-wave waveform of a ring type in accordance with a preferred embodiment of the present invention, wherein 4a is a deployment diagram of the time-varying traveling beat-wave waveform of the traveling beat-wave W ', and 4b is a deployment diagram of the amplitude-normalized traveling beat-wave W';
FIG. 5 is a schematic diagram of the operation principle of the preferred embodiment of the present invention in which the traveling wave state and the standing wave state of the flapping wave are in a small cycle, wherein a, b, c, d represent four time points in the standing wave phase, the forward traveling wave phase, the standing wave phase and the reverse traveling wave phase of the flapping wave respectively in the large cycle of the operation of the flapping wave;
FIG. 6 is a schematic structural view of a vibration actuator according to a preferred embodiment of the present invention;
FIG. 7 is a graph of motor stator acceleration amplitude versus frequency difference in accordance with the present invention;
FIG. 8 is a schematic view of the stator elastomer and piezoelectric ceramic structure of the present invention;
FIG. 9 is a sectional polarization diagram of the piezoelectric ceramic of the present invention.
In the figure: 1 is a vibration output interface, 2 is an annular stator elastomer, 3 is a hollow shaft, 4 is a friction material, 5 is piezoelectric ceramic, and 6 is a plastic wear-resistant sleeve.
Detailed Description
The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic views illustrating only the basic structure of the present invention in a schematic manner, and thus show only the constitution related to the present invention.
The frequency conversion vibration method of the invention is based on a traveling wave ultrasonic motorSpecifically, the principle of the traveling wave ultrasonic motor is to excite the stator elastomer to respond B by utilizing the inverse piezoelectric effect of the piezoelectric ceramiconA vibration mode, wherein a traveling wave continuously running in a certain direction is formed in the stator body, and finally, high frequency (more than 20KHz, so the motor is named as an ultrasonic motor) with a driving effect and micro-amplitude elliptical motion (the amplitude is a plurality of microns) are generated on the surface of the stator body; if the rotor is pressed on the elliptical motion output surface designed by the stator with a certain pre-pressure, the rotor can be driven to continuously operate by means of the friction force between the stator and the rotor, and the motion direction is always opposite to the operation direction of the traveling wave in the stator body.
The beat traveling wave required by the application is derived on the basis of the traveling wave, and the beat traveling wave is a driving mode different from the traveling wave. The traveling wave in the ultrasonic motor is composed of two phases B with same frequency and amplitude and phase difference of 90 DEG in space and timeonThe traveling wave is obtained by superposition of vibration modes, and is characterized in that the running direction of the traveling wave cannot be changed if the time phase difference of the two-phase driving signals is fixed, and when the time phase difference of the two-phase driving signals is fixed to be-90 degrees, the traveling wave runs anticlockwise, and the rotor rotates clockwise; when the time phase difference is fixed to be 90 degrees, the traveling wave runs clockwise, and the rotor rotates anticlockwise; the beat travelling wave is different from travelling wave in that it is composed of two phases of similar frequency, same amplitude and phase difference of 90 deg. in spaceonThe time phase difference of the two-phase vibration is continuously changed between 0-360 degrees due to the effect of beat frequency, so that the beat wave is characterized in that the running direction is periodically changed, and the frequency is the frequency difference of the two-phase driving signals.
Example 1:
based on the above, what the application needs to do first is to derive a theoretical formula of the traveling wave, which is specifically as follows:
the first step is as follows: writing a two-phase standing wave formula for synthesizing the traveling wave according to the traveling wave synthesis theory of the existing annular ultrasonic motor, and analyzing the relation between the phase difference of the two-phase standing waves and the operation direction of the synthesized traveling wave;
the existing standing wave formula is:
W1(θ,t)＝Asinnθcos2πft (1)
and (3) superposing the formula (1) and the formula (2) to obtain a synthetic traveling wave formula (3):
as can be seen from the formula (3),
when the phase difference of two phase standing wave time
Then, equation (3) becomes forward traveling wave equation (4):
W＝sin(nθ-ωt) (4)
when the two standing waves are time-phase-different
Then, equation (3) becomes reverse traveling wave equation (5):
W＝sin(nθ+ωt) (5)
the second step is that: and analyzing the relation between the forward and backward traveling wave particle motion direction and the waveform position to obtain a time-space partial derivative method as a criterion for judging the traveling wave running direction. The method specifically comprises the following steps: as shown in fig. 2, for the forward traveling wave, the downhill particle 1 of the forward traveling wave instantaneously moves upward, and the uphill particle 2 instantaneously moves downward, and as shown in fig. 3, for the reverse traveling wave, the downhill particle 3 of the reverse traveling wave instantaneously moves downward, and the uphill particle 4 instantaneously moves upward, so that the movement method of the waveform is determined according to the reversal of the particle movement and the position of the waveform where the particle is located, that is, the downhill particle of the forward traveling wave moves upward, and the uphill particle moves downward; the downward slope particles of the backward traveling wave move downward and the upward slope particles move upward, which are expressed by mathematical symbols as shown in tables 1 and 2
TABLE 1 forward traveling wave time-space partial derivative relationship
TABLE 2 inverse traveling wave time-space partial derivative relationship
When the time partial derivative and the space partial derivative of the traveling wave formula are of the same sign, the traveling wave is in the forward direction;
the third step: and respectively solving the partial derivatives of the forward traveling wave formula (4) and the reverse traveling wave formula (5) to obtain formulas (6) - (9):
obviously, the equations (6) and (7) have opposite signs, and the equations (8) and (9) have the same sign, so that a space-time partial derivative method for judging the traveling wave direction is obtained, as shown in table 3 below:
TABLE 3 space-time partial derivative method
Thus further proving the space-time partial derivative method of the traveling wave direction proposed in the second step;
the fourth step: obtaining two-phase standing wave formulas (10) and (11) of the beat travelling wave according to a synthesis formula of the travelling wave,
W1'＝sinnθcos(2πf1t+φ10) (10)
W2'＝cosnθcos(2πf2t+φ20) (11)
linearly superposing two-phase standing wave formulas (10) and (11) of the beat traveling wave to obtain a synthetic beat traveling wave formula (12) and enabling 2 pi f1＝ω1、2πf2＝ω2Obtaining a synthetic beat traveling wave formula W ═ W after synthesis1'+W2' is:
W'＝sinnθcos(2πf1t+φ10)+cosnθcos(2πf2t+φ20) (12)；
the fifth step: FIG. 4a is a development diagram of a beat wave waveform varying with time, suitable parameters are selected, a beat wave W' is plotted by taking a spatial position theta as an abscissa, each curve in FIG. 4a represents a waveform circumferential development diagram at a moment, and the difference between t1 and t3 at each moment is 2ms<1/10f1. The amplitude of the waveform can be seen to change along with time, so that the direction of the waveform cannot be judged by directly using a space-time partial derivative method; therefore, before the traveling wave direction judgment criterion is used, the amplitude normalization processing needs to be carried out on the beat traveling wave formula, the waveform motion direction information of the beat traveling wave is reserved, the waveform formula is analyzed, and at t0Time command: a ═ cos (ω)1t0+φ10)、B＝cos(ω2t0+φ20) Then, then
determining the direction of the beat traveling wave, and performing a space-time partial derivative method on the beat traveling wave formula subjected to amplitude normalization, namely solving a time and space first-order partial derivative of the formula (14):
in comparison of the formulas (15) and (16), the denominator is positive, and the second half of the molecular formula (15) is completely the same as the numerator of the formula (16), so that the symbol relationship between the formulas is determined by the first half of the numerator of the formula (15), that is, the formula (17)
H＝ω1sin(ω1t+φ10)cos(ω2t+φ20)-ω2cos(ω1t+φ10)sin(ω2t+φ20) (17)
After deformation, obtaining:
wherein Δ ω ═ ω1-ω2The difference between two phase circular frequencies is the working frequency of the ultrasonic motor is generally above 20kHz, so the ultrasonic motor has the advantages of simple structure, low cost and high efficiency
Thus:
H≈ω1sin(Δωt+(φ10-φ20)) (19)
formula (19) is a period of
Where Δ f is the difference between the natural frequencies of the two phases, the first half-cycle is positive and the second half-cycle isThe variation cycle and the frequency of the motion direction of the driving force output by the stator of the traveling wave motor are finally obtained, namely the variation cycle of the traveling wave motion direction is the reciprocal of the natural frequency difference of the two phases, and one half of the variation cycle is positive and the other half is reverse; the direction of the output driving force of the motor stator is opposite to the traveling wave direction, so that the direction of the output driving force of the stator of the traveling wave motor is finally determined to change in a regular period similar to a sine function, the frequency is the difference between two phases of driving frequencies, the schematic diagram of the waveform running rule is shown in fig. 5, wherein a, b, c and d represent four moments in a large running period of the traveling wave beating respectively and are respectively in a standing wave phase, a forward traveling wave phase, a standing wave phase and a reverse traveling wave phase of the traveling wave beating, and the four phases can appear in turn in sequence during the running of the traveling wave beating, and the period is the reciprocal of the frequency difference of the two phases of the standing.
It should be further explained that, for the ultrasonic motor, the adjustment of the steering can be realized by adjusting the time phase difference of the two phase driving signals, but in practice, the adjustment of the phase difference by the driver is discontinuous, that is, the phase difference of the two phase signals is not continuously changed, but the phase difference of the two signals is continuously changed during the operation by the two phase beat frequency signals. Assuming a two-phase sinusoidal signal w1、w2Respectively at a frequency of f1And f2The initial phase difference is 0. When the two signals are out of phase by 2 π, i.e., when w1Ratio w2One cycle ahead, equation (20) is satisfied:
f1t-f2t＝1(20)
thus obtaining
So the phase difference between the two signals varies continuously within 0-2 pi, and the period is:
where Δ f ═ f1-f2This is consistent with the above derived variation cycle of the running direction of the flapping wave; the continuous adjustment of the phase is important here because of the sudden change in phaseInstead, abrupt changes in waveform amplitude can be caused, resulting in noise during motor operation, and continuous changes in phase difference can avoid this problem.
Example 2:
then, the obtained beating traveling wave theory is applied to an annular traveling wave rotary ultrasonic motor, a novel vibration actuator designed based on the frequency conversion vibration method is designed by utilizing the theory, and as shown in figure 6, the design is only schematic in principle, the size can be large or small (D: 5-60mm, H: 3-5mm), and the beating traveling wave theory can be embedded into various systems needing vibration tactile feedback; such as handheld smart devices, outdoor large touch screen display devices, and wearable haptic feedback devices.
The vibration output device comprises a hollow shaft 3, wherein a stator elastic body ceramic plate assembly shown in fig. 8 is sleeved on the hollow shaft 3, the bottom surface of a vibration output interface 1 is fixedly arranged on the hollow shaft 3, the hollow shaft 3 is fixedly connected with the vibration output interface 1 through a screw, and the surface of an annular stator elastic body 2 abuts against the bottom surface of the vibration output interface 1 with a certain pre-pressure while the hollow shaft 3 axially locks the annular stator elastic body 2;
the piezoelectric ceramic 5 is laid on the bottom surface of the annular stator elastic body 2 away from the vibration output interface 1, as shown in fig. 9, the piezoelectric ceramic 5 is divided into two symmetrical parts, namely an area a and an area B, on the surface, and the area a and the area B each comprise two groups of positively and negatively polarized ceramic plates. The ceramic plate polarized in this way can excite the ground n-order bending vibration mode of the stator elastic body, wherein the vibration modes excited by the regions a and B are the above-mentioned two-phase standing waves. (ii) a
Paving a friction material 4 between the bottom surface of the vibration output interface 1 and the surface of the annular stator elastic body 2; a plastic wear-resistant sleeve 6 is arranged between the bullet body and the hollow shaft 3, and the plastic wear-resistant sleeve 6 is also sleeved on the hollow shaft 3;
the above preferred embodiment uses rolling bearings or plastic sliding bearings for the isolation of the force transmission from the moving and supporting parts. And a plastic wear-resistant material commonly used for an ultrasonic motor is stuck between the vibration output interface 1 plate and the annular stator elastic body 2 and used for isolating dry friction between the metal bodies and improving the output performance of the vibration actuator. The specific implementation method of the beat traveling wave driving mode is that sine signals with different frequencies and same amplitudes are respectively applied to two groups of ceramic plates attached to the stator elastic body, so that beat traveling waves with periodically changed running directions can be generated in the annular stator elastic body 2, and a driving force with periodically changed directions is generated on a designed motion output surface of the annular stator elastic body 2; meanwhile, in the vibration actuator provided by the invention, under the driving of the beat-wave driving mode, the annular stator elastic body 2 can periodically change the rotating direction under the driving of the self-generated driving force, and the frequency is the difference of the frequencies of the two-phase driving signals. When the frequency difference increases, the stator angle also becomes smaller, for example, when the frequency difference reaches 20Hz, the stator steering switching frequency also reaches 20Hz, and the amplitude of the stator angle becomes smaller. But the amplitude of the acceleration of the stator rotation increases much more due to the high frequency. The relationship between the angular acceleration and the frequency difference is shown in fig. 7, and it can be seen from the graph that the amplitude of the angular acceleration of the motor and the frequency difference are in a linear relationship, so if the frequency difference is increased, the amplitude of the angular acceleration of the stator is also increased;
from the inertial force equation:
FI＝-Jα(20)
the acting force of the stator to the vibration output interface 1 plate is obtained as FIWhere J is the moment of inertia of the stator and α is the angular acceleration amplitude of the stator, and therefore, by appropriately increasing the vibration frequency of the motor, the sense of vibration can be increased.
In summary, the variable frequency vibration method provided by the invention based on the beat traveling wave driving principle can change the original single direction rotation of the annular ultrasonic motor into the operation mode of forward and reverse switching, and can realize quick response.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The meaning of "and/or" as used herein is intended to include both the individual components or both.
The term "connected" as used herein may mean either a direct connection between components or an indirect connection between components via other components.
In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims (8)
1. A frequency conversion vibration method capable of shortening response time is characterized in that: the method comprises the following steps:
the first step is as follows: writing a two-phase standing wave formula for synthesizing the traveling wave according to the traveling wave synthesis theory of the existing annular ultrasonic motor, and analyzing the relation between the phase difference of the two-phase standing waves and the operation direction of the synthesized traveling wave;
the second step is that: and analyzing the relation between the forward and backward traveling wave particle motion direction and the waveform position to obtain a time-space partial derivative method as a criterion for judging the traveling wave running direction.
The third step: further respectively solving time and space partial derivatives of the forward and reverse traveling wave formulas to prove the correctness of the second step according to the space-time partial derivative method;
the fourth step: writing a superposition formula of the beat travelling wave according to the principle that the standing wave is superposed into the travelling wave, namely changing the superposition of the two-phase standing wave with the same amplitude and frequency and the phase difference of 90 degrees in space and time into the superposition of the two-phase standing wave with the similar amplitude and frequency, and superposing the two-phase standing wave with the phase difference of 90 degrees in space to obtain the formula of the travelling wave;
the fifth step: analyzing the running rule of the beat traveling wave by adopting a space-time partial derivative method, firstly carrying out amplitude normalization processing on a beat traveling wave formula, reserving the waveform motion direction information of the beat traveling wave, secondly obtaining the running direction change rule of the beat traveling wave by adopting the space-time partial derivative method on the beat traveling wave after the amplitude normalization, and finally obtaining the motion direction change period and the frequency of the stator output driving force of the rotary traveling wave ultrasonic motor under the drive mode of the beat traveling wave.
2. The variable frequency vibration method capable of shortening response time according to claim 1, wherein: according to the standing wave formula of the existing annular ultrasonic motor:
W1(θ,t)＝Asinnθcos2πft (1)
wherein,
in order to be the phase difference,
the formula (1) and the formula (2) are superposed to obtain a synthetic traveling wave two-phase standing wave formula
When the two standing waves are time-phase-different
Then, equation (3) becomes the forward traveling wave equation:
W＝sin(nθ-ωt) (4)
when the two standing waves are time-phase-different
Then, the formula (3) is changed into a reverse traveling wave formula
W＝sin(nθ+ωt) (5)
3. The variable frequency vibration method capable of shortening the response time according to claim 2, characterized in that: according to the position relation between the moving direction of forward and backward traveling wave mass points and the waveform, the moving method of the waveform is judged according to the backward direction of the mass points and the position of the waveform of the mass points, namely when the time partial derivative and the space partial derivative of the traveling wave formula are of different signs, the traveling wave is in the forward direction, and when the time partial derivative and the space partial derivative of the traveling wave formula are of the same sign, the traveling wave is in the backward direction.
4. The variable frequency vibration method capable of shortening response time according to claim 3, wherein: and respectively solving the partial derivatives of the forward traveling wave formula (4) and the reverse traveling wave formula (5) to obtain formulas (6) - (9):
obviously, the equations (6) and (7) have opposite signs, and the equations (8) and (9) have the same sign, so that a space-time partial derivative method for judging the traveling wave direction is obtained.
5. The variable frequency vibration method capable of shortening response time according to claim 4, wherein: obtaining two-phase standing wave formulas (10) and (11) of the beat traveling wave through the obtained forward traveling wave formula and the reverse traveling wave formula,
W1'＝sinnθcos(2πf1t+φ10) (10)
W2'＝cosnθcos(2πf2t+φ20) (11)
wherein the frequencies of the two-phase sinusoidal signals are respectively f1And f2，
Linearly superposing two-phase standing wave formulas of the beat traveling wave to obtain a synthetic beat traveling wave formula (12) and enabling 2 pi f1＝ω1、2πf2＝ω2After synthesis, W ═ W is obtained1'+W2' is:
W'＝sinnθcos(2πf1t+φ10)+cosnθcos(2πf2t+φ20) (12)。
6. the variable frequency vibration method capable of shortening response time according to claim 5, wherein: the step of performing amplitude normalization processing on the traveling wave formula is as follows: at t0Time command: a ═ cos (ω)1t0+φ10)、B＝cos(ω2t0+φ20) Then, then
the first partial derivative in time and space is calculated for equation (14):
in comparison of the formulas (15) and (16), the denominator is positive, and the second half of the molecular formula (15) is completely the same as the numerator of the formula (16), so that the symbol relationship between the formulas is determined by the first half of the numerator of the formula (15), that is, the formula (17)
H＝ω1sin(ω1t+φ10)cos(ω2t+φ20)-ω2cos(ω1t+φ10)sin(ω2t+φ20) (17)
After deformation, obtaining:
wherein Δ ω ═ ω1-ω2The difference between two phase circular frequencies is the working frequency of the ultrasonic motor is generally above 20kHz, so the ultrasonic motor has the advantages of simple structure, low cost and high efficiency
Thus:
H≈ω1sin(Δωt+(φ10-φ20)) (19)
formula (19) is a period of
The sine function of (1), wherein Δ f is the difference between two natural frequencies, the first half cycle is positive, and the second half cycle is negative, so that the variation cycle of the running direction of the beat traveling wave is the reciprocal of the natural frequency difference of the two phases, and one half is positive and the other half is reverse; because the direction of the output driving force of the motor stator is opposite to the traveling wave direction, the direction of the output driving force of the stator of the traveling wave motor is finally determined to change in a regular cycle similar to a sine function, and the frequency is the difference between two phase driving frequencies.
7. A vibration actuator designed based on the variable frequency vibration method is characterized in that: the vibration output interface is fixedly arranged at the top of the hollow shaft through a screw, the hollow shaft is axially locked to the annular stator elastic body, and meanwhile, the annular stator elastic body generates pre-pressure to abut against the vibration output interface;
a friction material is laid on the contact surface of the annular stator elastomer and the vibration output interface;
piezoelectric ceramics with partitioned polarization are laid on the end face, far away from the vibration output interface, of the annular stator elastic body;
a plastic wear-resistant sleeve is arranged between the stator elastic body and the hollow shaft, and the plastic wear-resistant sleeve is sleeved on the hollow shaft.
8. The vibration actuator designed based on the variable frequency vibration method according to claim 7, wherein: the surface of the piezoelectric ceramic is divided into two symmetrical parts, namely an area A and an area B, wherein the area A and the area B respectively comprise four ceramic plates.
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