Non-contact passive angle sensor based on piezoelectric effect

Abstract

The invention discloses a non-contact passive angle sensor based on a piezoelectric effect, and belongs to the field of sensors. The problem that an existing passive angle sensor is poor in anti-interference performance due to the fact that the existing passive angle sensor is affected by environmental factors and material characteristics is solved. According to the scheme, a stepped shaft is arranged in the center of a containing cavity of a shell, and a wave point wheel and a planetary gear transmission mechanism are sequentially installed on the stepped shaft; grooves are formed in the upper end and the lower end of the containing cavity of the shell and used for installing the piezoelectric sensing module, and the normal lines of the two grooves form an alpha angle. The piezoelectric sensing module comprises piezoelectric units and a piezoelectric plate support, m piezoelectric units are axially installed on the piezoelectric plate support side by side, and a permanent magnet iron sheet is attached to one side of each piezoelectric unit. M circles of permanent magnet sheets are attached to the periphery of the wave point wheel, are sequentially arranged in a staggered mode and repel the permanent magnet sheets on the piezoelectric units during rotation, so that the piezoelectric units deform in the normal direction, and potential difference is formed between the upper surfaces and the lower surfaces of the piezoelectric sheets; the rotation angle of the planet carrier is converted into the rotation angle of the wave point wheel at a fixed transmission ratio, and the angle is represented by an intermittent voltage signal inductively output by the piezoelectric unit.

Description

Technical Field

[0001] The present invention relates to a non-contact passive angle sensor based on the piezoelectric effect, belonging to the field of sensors. Background Art

[0002] The behavior monitoring of human movement plays a quite important role in the fields of healthcare, limb function rehabilitation, sports training, etc. The core of human movement monitoring lies in the monitoring of joint angles, which is of great significance for evaluating an individual's movement state, formulating personalized training plans, and diagnosing potential health problems. At present, in the industrial field, active angle sensors, especially Hall angle sensors and magnetoresistive angle sensors, etc., have extremely wide applications. However, from the macroscopic perspective of social energy management, although the energy consumption of a single sensor device is negligible, the large-scale deployment of sensor networks, such as in the application of the Internet of Things, involves hundreds of millions of devices. These sensors are widely distributed and it is difficult to achieve centralized power supply. Although the existing battery-powered solutions are widely used, they still face multiple challenges such as limited service life, serious environmental pollution, and low energy utilization efficiency.

[0003] To overcome the above defects, researchers have explored many wearable passive sensor devices, and their research focuses mainly on the application of flexible materials and the improvement of wearing comfort. Such sensors mainly measure joint angles through the triboelectric effect and the piezoelectric effect, and their characteristic is that the amplitude of the output voltage signal is directly related to the change of the joint angle. However, in practical applications, the amplitude of the output voltage signal is affected and interfered by many factors, resulting in significant differences in the amplitude of the output voltage signal even when the joint angles are the same.

[0004] Specifically, in terms of external environmental factors, the piezoelectric constant of the piezoelectric material will be affected by temperature fluctuations, resulting in signal drift; in a high-humidity environment, the surface charges of the triboelectric material are easily neutralized by water molecules, resulting in signal attenuation; in addition, the adhesion and accumulation of skin oil, sweat, or dust on the surface of the triboelectric material will all lead to a decrease in the charge generation efficiency.

[0005] And in terms of internal material properties, the aging and fatigue of the material will inevitably occur during long-term use. For example, the wear on the surface of the triboelectric material will lead to a decrease in the charge generation efficiency; the piezoelectric material may also show polarization attenuation after long-term stress; in addition, the inherent hysteresis characteristic of piezoelectric ceramics makes there be a large error when measuring the joint angles of reciprocating movements.

[0006] In view of the above technical challenges, it becomes particularly important to design a passive and strongly anti-interference non-contact angle sensor. This innovation not only is expected to solve the problem of distributed power supply in the Internet of Things era, but also will bring new development opportunities to angle measurement technologies, especially angle measurement technologies in wearable devices, and expand their application fields. Summary of the Invention

[0007] In order to solve the problems of unstable output voltage signals and poor anti-interference performance of existing wearable angle sensors due to the influence of external environmental factors and internal material properties, the present invention provides a non-contact passive angle sensor based on the piezoelectric effect.

[0008] The non-contact passive angle sensor based on the piezoelectric effect of the present invention comprises a planetary gear transmission mechanism, a housing 4, a wave-point wheel 5 and a piezoelectric sensing module;

[0009] The housing 4 is provided with a cavity, the center of which is provided with a stepped shaft, on which the wavy wheel 5 and the planetary gear transmission mechanism are sequentially mounted;

[0010] The housing 4 has grooves 4-1 at the upper and lower ends for mounting the piezoelectric sensor module. The normals of the upper and lower grooves 4-1 form an angle α.

[0011] The piezoelectric sensing module includes a piezoelectric unit 6 and a piezoelectric sheet support 7. Each piezoelectric sheet support 7 is axially mounted with m piezoelectric units 6 in parallel. An aluminum sheet is attached to the back of the piezoelectric unit 6, and a permanent magnet sheet is attached to the front of the piezoelectric unit 6 facing the wave wheel 5.

[0012] The circumference of the wavy wheel 5 is affixed with m circles of permanent magnets. The permanent magnets in each circle are evenly distributed and staggered at a phase angle of β. The m circles of permanent magnets in the wavy wheel 5 correspond one-to-one with the m permanent magnets on the piezoelectric unit. During rotation, the permanent magnets of the wavy wheel 5 provide a repulsive force to the piezoelectric unit 6.

[0013] The permanent magnets on each of the five circles of the polka dot wheel form an angle φ with each other;

[0014] The rotation angle of the planet carrier 1 is converted into the rotation angle of the wave-point wheel 5 at a fixed transmission ratio. The angle is represented by the intermittent voltage signal sensed and output by the piezoelectric unit.

[0015] Preferably, the planetary gear transmission mechanism includes a planet carrier 1, a ring gear 3, a sun gear 8 and planet gears 9;

[0016] The wave-point wheel 5, sun wheel 8 and planet carrier 1 are sequentially mounted on the central stepped shaft of the housing 4. The sun wheel 8 is fixedly connected to the wave-point wheel 5 and rotates coaxially. A fixing buckle 10 is provided on the outer side of the planet carrier 1 to fix the axial position of the planet carrier 1.

[0017] Three planetary gears 9 are mounted on the planetary carrier 1 , and the axial positions of the planetary gears 9 are fixed by another fixing buckle 10 ;

[0018] The three planetary gears 9 mesh with the outer ring gear 3 and the inner sun gear 8;

[0019] The inner side of the ring gear 3 is fixed to the housing 4, and the outer side is covered with a retaining ring 2;

[0020] The rotational movement of the joint is input from the planet carrier 1, transmitted to the sun gear 8 via the planet gears 9, and then drives the dot wheel 5 to rotate.

[0021] Preferably, the magnetization directions of the permanent magnet sheets on the dot wheel 5 and the piezoelectric unit are both radially magnetized; the polarity of the outer side of the permanent magnet sheet on the dot wheel 5 is the same as the polarity of the outer side of the permanent magnet sheet on the piezoelectric unit 6.

[0022] Preferably, the value range of m is from 2 to 5.

[0023] Preferably, m = 3.

[0024] Preferably, α = 1° - 5°.

[0025] Preferably, α = 2°.

[0026] Preferably, the phase angle β = 3° - 9°.

[0027] Preferably, the phase angle β = 4°.

[0028] Preferably, φ = 9° - 18°.

[0029] Advantages of the present invention:

[0030] The present invention adopts the design of a passive sensor, and its core sensing component gets rid of the dependence on an external power source, thereby broadening the application scenarios of the sensor and enhancing the convenience of use.

[0031] The present invention innovatively adopts the waveform counting method to measure the joint angle, rather than the method that directly depends on the piezoelectric signal amplitude in the traditional design. This method effectively avoids the measurement error caused by temperature drift of the piezoelectric material in different temperature environments, and also solves the influence of polarization attenuation of the material after long-term stress and piezoelectric hysteresis effect in the reciprocating rotational motion on the measurement accuracy, ensuring the high accuracy and stability of the angle measurement.

[0032] By introducing the permanent magnet sheet, the present invention changes the force acting mode on the piezoelectric unit from the traditional contact force to the non-contact magnetic force, and successfully realizes the non-contact operation of the core sensing component. This change significantly reduces the physical wear of the material and can extend its service life.

[0033] Compared with the traditional passive angle sensor that only shows a linear relationship between the voltage signal and the joint angle within a limited angle range, resulting in the defect of limited angle range, the present invention can achieve linear measurement within 180°, ensuring the uniformity and consistency of the measurement accuracy throughout the entire range. Description of the Drawings

[0034] Figure 1 is a schematic diagram of the overall structure of a non-contact passive angle sensor based on the piezoelectric effect according to the present invention;

[0035] Figure 2 is an exploded schematic diagram of the overall structure of a non-contact passive angle sensor based on the piezoelectric effect according to the present invention;

[0036] Figure 3 is a schematic diagram of the spatial structure of the dot wheel and the piezoelectric array;

[0037] Figure 4 is a trigger timing diagram of the piezoelectric array;

[0038] Figure 5 is a schematic diagram of the spatial structure of the dot wheel and the piezoelectric array after reducing the angular resolution;

[0039] Figure 6 is a schematic diagram of the spatial structure of the dot wheel and the piezoelectric array after improving the angular resolution;

[0040] Figure 7 is a schematic diagram of the piezoelectric unit structure. Detailed implementation manners

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0042] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0043] Next, the present invention will be further described in conjunction with the accompanying drawings and specific embodiments, but it is not a limitation of the present invention.

[0044] Detailed implementation manner one: Next, in conjunction with Figures 1 to 7 This implementation manner will be described. A non-contact passive angle sensor based on the piezoelectric effect described in this implementation manner includes a planetary gear transmission mechanism, a housing 4, a dot wheel 5, and a piezoelectric sensing module;

[0045] The housing 4 is provided with a cavity, and there is a stepped shaft at the center of the cavity. The dot wheel 5 and the planetary gear transmission mechanism are sequentially installed on the stepped shaft;

[0046] Grooves 4-1 are provided at the upper and lower ends of the cavity of the housing 4 for installing the piezoelectric sensing module, and the normal lines of the upper and lower grooves 4-1 form an angle α;

[0047] The piezoelectric sensing module includes a piezoelectric unit 6 and a piezoelectric sheet bracket 7. Along the axial direction, m piezoelectric units 6 are installed side by side on each piezoelectric sheet bracket 7. An aluminum sheet is pasted on the back of the piezoelectric unit 6, and a permanent magnet sheet is pasted on the front of the piezoelectric unit 6 facing the dot wheel 5.

[0048] m circles of permanent magnet sheets are pasted on the circumference of the dot wheel 5. The permanent magnet sheets in each circle are evenly distributed. The m circles of permanent magnet sheets are arranged in sequence with a phase angle of β. The m circles of permanent magnet sheets on the dot wheel 5 correspond to the m permanent magnet sheets on the piezoelectric unit one by one. When rotating, the permanent magnet sheets of the dot wheel 5 provide a repulsive force for the piezoelectric unit 6.

[0049] The permanent magnet sheets on each circle of the circumference of the dot wheel 5 form an angle of φ with each other.

[0050] The rotation angle of the planet carrier 1 is converted into the rotation angle of the dot wheel 5 at a fixed transmission ratio, and this angle is characterized by the intermittent voltage signal induced and output by the piezoelectric unit.

[0051] The planetary gear transmission mechanism includes a planet carrier 1, a ring gear 3, a sun gear 8, and planet gears 9.

[0052] The dot wheel 5, the sun gear 8, and the planet carrier 1 are sequentially installed on the central stepped shaft of the cavity of the housing 4. The sun gear 8 is fixedly connected to the dot wheel 5 and rotates coaxially. A fixed buckle 10 is provided outside the planet carrier 1 to fix the axial position of the planet carrier 1.

[0053] Three planet gears 9 are installed on the planet carrier 1, and another fixed buckle 10 is used to fix the axial position of the planet gears 9.

[0054] The three planet gears 9 are meshed with the external ring gear 3 and the internal sun gear 8.

[0055] The inner side of the ring gear 3 is fixed to the housing 4, and the outer side is covered with a retaining ring 2.

[0056] The rotational movement of the joint is input from the planet carrier 1, transmitted to the sun gear 8 via the planet gears 9, and then drives the dot wheel 5 to rotate.

[0057] The magnetization directions of the permanent magnet sheets of the dot wheel 5 and the permanent magnet sheets on the piezoelectric unit are both radially magnetized; the polarity of the outer side of the permanent magnet sheet of the dot wheel 5 is the same as the polarity of the outer side of the permanent magnet sheet on the piezoelectric unit 6.

[0058] The value range of m is from 2 to 5, and the preferred value is m = 3.

[0059] α = 1° to 5°, and the preferred value is α = 2°.

[0060] The phase angle β = 3° to 9°, and the preferred value is β = 4°.

[0061] φ = 9° to 18°, and the preferred value is φ = 12°.

[0062] The outer side of the housing 4 extends as a mounting handle, on which there are mounting holes, and the inner side of the mounting handle protrudes to avoid interference with the mounting handle of the planet carrier 1.

[0063] The working principle of the piezoelectric sensor of the present invention will be described below with an example.

[0064] m = 3, and every three piezoelectric units 6 are installed in a group in the piezoelectric sheet bracket 7. Refer to Figure 3 , the piezoelectric units installed in the upper groove of the cavity are the first piezoelectric unit 6-1, the third piezoelectric unit 6-3, and the fifth piezoelectric unit 6-5 respectively. Correspondingly, the piezoelectric units in the lower groove are the second piezoelectric unit 6-2, the fourth piezoelectric unit 6-4, and the sixth piezoelectric unit 6-6 respectively. Among them, the first piezoelectric unit 6-1 and the second piezoelectric unit 6-2 are arranged oppositely and correspond to the first ring of permanent magnet sheets on the circumference of the dot wheel 5; the third piezoelectric unit 6-3 and the fourth piezoelectric unit 6-4 are arranged oppositely and correspond to the second ring of permanent magnet sheets on the circumference of the dot wheel 5; the fifth piezoelectric unit 6-5 and the sixth piezoelectric unit 6-6 are arranged oppositely and correspond to the third ring of permanent magnet sheets on the circumference of the dot wheel 5.

[0065] β = 4°, the permanent magnet sheets on each circle of the circumference of the dot wheel 5 are mutually at an angle of φ = 12°, a total of three circles, and there is also a phase angle of 4° between the circles.

[0066] Determine the transmission path and transmission ratio of the planetary gear transmission mechanism. The sun gear 8, the planet carrier 1, and the ring gear 3 of the planetary gear mechanism can theoretically all be used as angle inputs or outputs. Therefore, there are theoretically six transmission paths. However, considering that the ring gear 3 is on the outermost layer and it is not convenient to make a movable structure, the ring gear 3 is fixed on the housing 4, and the planet carrier 1 and the sun gear 8 are used as angle inputs and outputs respectively. Among them, the transmission path of the sun gear 8 input and the planet carrier 1 output is a speed reduction transmission, and the transmission path of the planet carrier 1 input and the sun gear 8 output is a speed increase transmission. Since it is necessary to amplify the input angle, that is, a speed increase transmission is required, the transmission path is determined to be the planet carrier 1 input and the sun gear 8 output. Let the pitch circle radius of the sun gear 8 be r1 and the pitch circle radius of the planet gear 9 be r2, then the transmission ratio of this transmission form is

[0067]

[0068] Considering that the overall size of the sensor should not be too large, so let r1 = r2, and the calculated transmission ratio i = 4.

[0069] Determine the angle between the normal lines of the upper and lower grooves of the cavity of the housing 4 and the angle between the permanent magnet sheets. Since the angular resolution is 0.5°, and the transmission ratio is 4, it can be determined that for every 0.5° rotation of the planet carrier 1, the dot wheel 5 will rotate 2°, that is, a piezoelectric signal needs to be generated every 2°. In theory, only one piezoelectric unit 6 can be used, and a permanent magnet sheet is arranged every 2° on the circumference of the dot wheel 5 to achieve the effect. However, this configuration requires the diameter of the dot wheel 5 to be large enough to accommodate the magnet layout, or requires the permanent magnet sheet to be miniaturized to the limit size. The former will cause the overall structure size of the sensor to be too large and exceed the engineering application limit, while the latter will greatly reduce the repulsive force due to the sudden drop in magnetic flux density, resulting in the inability to effectively trigger the piezoelectric signal. Therefore, this scheme is unreasonable. Therefore, the present invention adopts the method of arranging a piezoelectric unit array, so as to increase the angle between the permanent magnet sheets without changing the angular resolution.

[0070] Six piezoelectric units 6 successively generate piezoelectric waveform signals when the dot wheel 5 rotates (see Figure 4 ), and the joint angle input can be obtained by counting the number of waveforms, and the forward and reverse rotations can be judged by judging the triggering timing of the piezoelectric array.

[0071] Transmission relationship: The rotation angle is input by the planet carrier 1, transmitted to the sun gear 8 via the planet gear 9, and the sun gear 8 is fixedly connected to the dot wheel 5. Therefore, the angular rotation of the joint is converted into the rotation of the dot wheel 5, and then into the intermittent voltage signal of the piezoelectric unit 6. The transmission ratio of the planetary gear mechanism is 4, that is, for every 0.5° rotation of the planet carrier 1, the dot wheel 5 will rotate 2°, and a piezoelectric unit 6 is triggered to generate a piezoelectric signal. Therefore, the angular resolution of this sensor is 0.5°.

[0072] It should be noted that the number of piezoelectric units 6 and the arrangement form of the piezoelectric units 6 in the present invention can be changed according to the actual angular resolution requirements. If the requirement for angular resolution is not particularly high, the number of piezoelectric units 6 can be appropriately reduced, and the transmission ratio, the angle between the normal lines of the upper and lower grooves of the cavity of the housing 4, and the angle between the permanent magnet sheets can be rematched, as Figure 5 shown. If it is necessary to further improve the angular resolution, the number of piezoelectric units 6 can also be appropriately increased, and it is not necessary to only arrange the piezoelectric units 6 on the upper and lower sides of the cavity of the housing 4, as Figure 6 shown.

[0073] The specific structure of the piezoelectric unit 6 is as Figure 7 shown. The piezoelectric sheet can be PZT-5H with flanged electrodes, and the substrate can be an aluminum sheet or other metal sheets that can improve the stiffness of the piezoelectric unit. If a piezoelectric sheet with flanged electrodes is selected, the adhesive between the piezoelectric sheet and the base layer can be a non-conductive adhesive.

[0074] Although the present invention has been described herein with reference to particular embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Accordingly, it should be understood that numerous modifications may be made to the exemplary embodiments, and other arrangements may be devised, without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with separate embodiments may be used in other described embodiments.

Claims

1. A non-contact passive angle sensor based on the piezoelectric effect, characterized in that, It comprises a planetary gear transmission mechanism, a housing (4), a wave-point wheel (5) and a piezoelectric sensor module; The housing (4) is provided with a cavity, a stepped shaft is provided at the center of the cavity, and the wave-point wheel (5) and the planetary gear transmission mechanism are sequentially mounted on the stepped shaft; Grooves (4-1) are provided at the upper and lower ends of the housing (4) for mounting the piezoelectric sensor module, and the normals of the upper and lower grooves (4-1) form an angle α; The piezoelectric sensing module comprises a piezoelectric unit (6) and a piezoelectric sheet support (7), wherein m piezoelectric units (6) are mounted in parallel along the axial direction on each piezoelectric sheet support (7), an aluminum sheet is adhered to the back of the piezoelectric unit (6), and a permanent magnet sheet is adhered to the front of the piezoelectric unit (6) facing the wave point wheel (5); The circumference of the wavy wheel (5) is pasted with m circles of permanent magnet sheets, the permanent magnet sheets of each circle are evenly distributed, and the m circles of permanent magnet sheets are staggered in sequence at a phase angle of β. The positions of the m circles of permanent magnet sheets of the wavy wheel (5) correspond one-to-one to the positions of the m permanent magnet sheets on the piezoelectric unit. When the wavy wheel (5) rotates, the permanent magnet sheets provide a repulsive force for the piezoelectric unit (6); The permanent magnets on each circle of the wavy wheel (5) form an angle φ with each other; The rotation angle of the planet carrier (1) is converted into the rotation angle of the wave-point wheel (5) at a fixed transmission ratio, and the angle is represented by the intermittent voltage signal induced and output by the piezoelectric unit.

2. The non-contact passive angle sensor based on the piezoelectric effect according to claim 1, characterized in that The planetary gear transmission mechanism comprises a planet carrier (1), a ring gear (3), a sun gear (8) and planet gears (9); The wave-point wheel (5), the sun wheel (8) and the planetary carrier (1) are sequentially mounted on the central stepped shaft of the housing (4); the sun wheel (8) and the wave-point wheel (5) are fixedly connected and rotate coaxially; a fixing buckle (10) is provided on the outer side of the planetary carrier (1) to fix the axial position of the planetary carrier (1); Three planetary gears (9) are mounted on the planetary carrier (1), and the axial positions of the planetary gears (9) are fixed by another fixing buckle (10); The three planetary gears (9) mesh with the outer ring gear (3) and the inner sun gear (8); The inner side of the gear ring (3) is fixed to the housing (4), and the outer side is covered by the retaining ring (2); The joint rotational motion is inputted by the planetary frame (1), transmitted to the sun gear (8) via the planetary gear (9), and then drives the wave point wheel (5) to rotate.

3. The non-contact passive angle sensor based on the piezoelectric effect according to claim 1, characterized in that, The magnetization directions of the permanent magnet pieces of the wavy wheel (5) and the permanent magnet pieces on the piezoelectric unit are both radial magnetization; the polarity of the outward-facing side of the permanent magnet pieces of the wavy wheel (5) is the same as the polarity of the outward-facing side of the permanent magnet pieces on the piezoelectric unit (6).

4. The non-contact passive angle sensor based on the piezoelectric effect according to claim 2, characterized in that, The value of m ranges from 2 to 5.

5. The non-contact passive angle sensor based on the piezoelectric effect according to claim 4, wherein m＝3。 6. The non-contact passive angle sensor based on the piezoelectric effect according to claim 2, wherein α＝1°～5°。 7. The non-contact passive angle sensor based on the piezoelectric effect according to claim 6, characterized in that, α＝2°。 8. The non-contact passive angle sensor based on the piezoelectric effect according to claim 2, characterized in that, Phase angle β = 3°~9°.

9. The non-contact passive angle sensor based on the piezoelectric effect according to claim 8, characterized in that Phase angle β = 4°.

10. The non-contact passive angle sensor based on the piezoelectric effect according to claim 2, characterized in that, φ=9°~18°.

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