Bending sensor based on magnetic film

Abstract

The utility model relates to a bending sensor based on a magnetic film. The sensor comprises a magnetic film, a tunnel magnetoresistance sensor and a flexible circuit board, wherein the two tunnel magnetoresistance sensors are fixed on the flexible circuit board at intervals, the flexible circuit board is covered with the magnetic film, and the tunnel magnetoresistance sensors are wrapped in the magnetic film; the model number of the tunnel magnetoresistance sensor is TMR2003. Inspired by the human skin, the bending sensor uses the magnetic film and the flexible printed circuit board, so that the finger bending degree is detected.

Description

Technical Field

[0001] The utility model belongs to the field of bending sensors, and in particular relates to a bending sensor based on a NdFeB magnetic film. Background Art

[0002] With the rapid development of artificial intelligence and robotics, wearable devices have become one of the hot topics for scientists to study. Among them, bend sensors, as a type of wearable device, have also received widespread attention. Bend sensors can accurately detect the bending angle of an object, and in the field of dynamic monitoring, they can also detect changes in the bending angle of an object. In practical applications, bend sensors can be used in wearable devices such as clothing and bracelets to detect human health and monitor human movement, and can be one of the means to prevent sports injuries and enhance exercise effects.

[0003] In the existing fields of human-computer interaction and intelligent equipment, the recognition and judgment of gestures play an increasingly important role. Gestures can make human-computer interaction convenient and fast, making people more comfortable with machine control and improving user satisfaction.

[0004] There are two main methods for implementing gesture recognition through devices: gesture recognition based on various wearable devices and gesture recognition based on visual images. Gesture recognition based on wearable devices is to collect hand movements through output signals from wearable devices such as gloves, and obtain hand changes through analysis to achieve gesture recognition. Gesture recognition based on visual images is to extract hand information from images taken by camera equipment to achieve gesture recognition. Compared with the latter, gesture recognition based on wearable devices has a faster response speed, more accurate recognition content, and wider applicability, so it has become a key research direction. Bend sensors are a widely used type of wearable sensing devices.

[0005] The current bending sensors include piezoresistive, triboelectric, and fiber optic sensors, which have some problems in sensitivity, flexibility, and stability. For example, the patent (202310419268.8) is a three-layer structure of NdFeB-PDMS magnetic film, PDMS substrate, and flexible printed circuit board. Magnetic electronic skin is made of NdFeB particles and dimethylsiloxane (PDMS) and applied to dynamic and static force detection, with a force measurement range of 0.05N-5N. However, due to the large Young's modulus of PDMS, the measurement accuracy is insufficient, and due to its poor flexibility, it is difficult to detect the bending angle. Utility Model Content

[0006] The purpose of the utility model is to improve some of the problems existing in the current sensors, and a bending sensor based on a magnetic film is designed. The bending sensor has a double-layer structure of a magnetic film bending sensor, and uses a tunnel magnetoresistance sensor element to detect the change in magnetic flux in the NdFeB-PDMS magnetic film to achieve bending angle detection. Inspired by human skin, the bending sensor uses a magnetic film and a flexible printed circuit board to detect the degree of finger bending.

[0007] The technical solution of the utility model is:

[0008] A bending sensor based on a magnetic film, the sensor comprising a magnetic film, a tunnel magnetoresistance sensor, and a flexible circuit board; wherein two tunnel magnetoresistance sensors are fixed on the flexible circuit board at intervals, the magnetic film covers the flexible circuit board, and wraps the tunnel magnetoresistance sensor therein;

[0009] The magnetic film is a NdFeB-silicone elastomer composite film, the mass ratio of the two is 3:1; the film thickness is 1.7-1.85 mm;

[0010] The model of the tunnel magnetoresistance sensor is TMR2003, the magnetic sensitive direction is horizontal, the size is 3mm×3mm×1.45mm, and the package form is SOT23-5; the distance between the two tunnel magnetoresistance sensors is 24-28mm.

[0011] The flexible circuit board is an FPC, and its size is 66mm×9mm×0.2mm.

[0012] The magnetic film is divided into five regions, and the directions of the magnetic fields in each region from left to right (horizontally) are upward, downward, upward, downward, and upward.

[0013] The essential features of this utility model are:

[0014] The magnetic film included in the utility model is a NdFeB-organic silicon magnetic film, which has improved flexibility; and the structure is optimized to a two-layer structure of NdFeB-organic silicon magnetic film and a flexible printed circuit board, which can be used to detect bending angles. When the sensor is bent, the magnetic film is deformed inside, causing the position and direction of the magnetic particles to change, thereby changing the magnetic flux density in the multipolar magnetized magnetic film. The tunnel magnetoresistance sensor senses the change in the magnetic field and converts this change into a voltage signal through the tunnel magnetoresistance effect. Subsequently, the voltage signal is output through the flexible printed circuit.

[0015] The beneficial effects of the utility model are:

[0016] The magnetic film has excellent flexibility and fit with the finger. This structure can enhance the sensitivity of the tunnel magnetoresistance sensor, thereby enhancing the practicality of the sensor. The utility model applies the magnetic film to the field of bending angle detection, providing a new method for bending angle detection; the utility model has a simple structure, small size, and thin thickness, and can be used in wearable devices with little impact on mobility; the preparation process of the utility model is simple, the cost is low, and no complex circuit is required to accurately identify the bending angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural disassembly diagram of the utility model.

[0018] Figure 2 It is a complete structural schematic diagram of the utility model.

[0019] Figure 3 This is the result of multi-pole magnetization along the thickness direction adopted by the utility model.

[0020] Figure 4 It is the position of magnetic particles inside the film when the utility model does not bend.

[0021] Figure 5 It is the position of magnetic particles inside the film when the utility model is bent.

[0022] Figure 6 It is the output voltage of the utility model at different bending angles.

[0023] Figure 7 It is the response and recovery time of the utility model when bending occurs.

[0024] Figure 8 The magnetic film used in the utility model is magnetized in a multi-polar manner along the thickness direction.

[0025] Markings in the attached figure: 1. magnetic film; 2. tunnel magnetoresistance sensor; 3. flexible circuit board; 4. connecting wire; 5. magnetic particles; 6. tunnel magnetoresistance sensor. DETAILED DESCRIPTION

[0026] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. The embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0027] The bending sensor based on the magnetic film of the utility model is as follows Figure 1 , Figure 2As shown, it includes a magnetic film 1, a tunnel magnetoresistance sensor 2, and a flexible circuit board 3; wherein two tunnel magnetoresistance sensors 2 are fixed on the flexible circuit board 3 at intervals, and the magnetic film 1 covers the flexible circuit board 3 and wraps the tunnel magnetoresistance sensor 2 therein;

[0028] The magnetic film 1 is composed of neodymium iron boron (Nd2Fe 14 B1) and silicone elastomer, the mass ratio of the two is 3:1; the preparation method is to mix NdFeB powder (particle size is 0.1-0.2mm) and silicone elastic prepolymer in a mass ratio of 3:1, stir for 25 minutes to make the NdFeB powder evenly distributed in the prepolymer, slowly pour the NdFeB-silicone elastic prepolymer into the prepared mold after stirring, and place it in a helium environment for 50 minutes to eliminate bubbles, squeeze out the excess material after finishing, and demold after curing at room temperature for 100 minutes to obtain a NdFeB-silicone film, magnetize it, and obtain a magnetic film;

[0029] It is divided into two layers, the upper layer is a multi-pole magnetized magnetic film used to simulate the epidermis of human skin. The neodymium iron boron magnet particles contained in the magnetic film simulate the Merkel cells in the skin and are used to transmit external stimuli; the lower layer is composed of a flexible printed circuit board and a tunnel magnetoresistive sensor welded on it, which is used to simulate the dermis of human skin. The sensor simulates the nerve endings in the skin, can sense changes in the upper layer and convert magnetic signal changes into electrical signals.

[0030] In order to ensure that the tunnel magnetoresistance sensor operates within the linear range, the magnetic film on the tunnel magnetoresistance sensor needs to maintain a certain thickness.

[0031] The thickness of the magnetic film has a great influence on the response performance of the sensor. If the thickness is too small, the tunnel magnetoresistance sensor cannot be supported and the life of the sensor will be reduced. If the thickness is too large, the sensitivity of the sensor will decrease and the movement of the finger will be affected. The size of the tunnel magnetoresistance sensor is 3mm×3mm×1.45mm, so the sensor thickness is set to 1.8mm so that the sensor has better overall performance.

[0032] The utility model provides a flexible bending sensor, wherein the magnetic film is a NdFeB-organic silicon elastomer composite film.

[0033] The utility model discloses a flexible bending sensor, wherein the model of the tunnel magnetoresistance sensor is TMR2003, the magnetic sensitive direction is the horizontal direction, the size is 3mm×3mm×1.45mm, and the packaging form is SOT23-5.

[0034] The utility model discloses a flexible bending sensor, wherein the flexible circuit board is an FPC, and the final size of the sensor is 66×9×1.9 mm.

[0035] The utility model discloses a flexible bending sensor, wherein the magnetic film is magnetized in a multi-pole manner along the thickness direction.

[0036] like Figure 5 As shown, when the sensor is bent, the upper magnetic film is deformed, and the position and direction of the magnetic particles in the film change laterally, thereby changing the magnetic flux density in the multipolarized magnetic film. At this time, the tunnel magnetoresistance sensor of the lower layer is used to sense the change in the magnetic flux density in the upper magnetic film, and the detected magnetic signal is converted into an electrical signal, which is output through the flexible circuit board below.

[0037] After the magnetic film is folded four times in the opposite direction, it is magnetized along the thickness direction. After magnetization, a rectangular array of magnetic fields will be formed on the horizontal plane. The magnetic field direction is divided into five regions, namely upward, downward, upward, downward, and upward. Figure 3 As shown. The magnetic directions of adjacent rectangles are opposite, and the magnetic field at the intersection of the rectangles is the largest. Therefore, the tunnel magnetoresistance sensor should be placed at the intersection of two adjacent rectangles. The tunnel magnetoresistance sensor is used to collect the magnetic field changes of the upper layer, and the magnetic signal is converted into an electrical signal and output through the FPC. The FPC is connected to the data acquisition card, and the data acquisition card is connected to the PC for signal processing and analysis.

[0038] In order to allow the sensor to sense bending more accurately and maximize the output, in practical applications, the intersection of adjacent rectangles of the magnetic field should be set at the finger joint. In this way, when the finger bends, it can be better detected and a higher voltage can be output, making data collection and processing easier. Therefore, the approximate size of the sensor should be determined by the finger size.

[0039] The utility model provides a bending sensor. When the output test is performed, the sensor is fixed directly below the push-pull force gauge and powered by a 5V DC regulated power supply. The transmission rod of the push-pull force gauge is rotated to deform the sensor. When the sensor is bent by an external force, the tunnel magnetoresistance sensor inside the sensor senses the change in magnetic flux in the upper film of the sensor, converts the change in magnetic flux into an electrical signal, and outputs it through the FPC. The FPC is connected to a data acquisition card for signal processing, and the data acquisition card is connected to a PC to display the collected data.

[0040] A bending sensor of the utility model has been repeatedly tested to verify the stability of the output and the accuracy of the experimental data. The test is carried out every 5° from 0° until it reaches 85°. After each bending to the specified angle, it stays for about 5 seconds to stabilize the output, and then randomly bends at a larger angle. During the entire repeated test process, the sensor unit maintains good output characteristics. At 0-75°, the output voltage of the sensor changes significantly with the change of the bending angle, and the output voltage changes when the subsequent angle changes are not obvious, so the measurement range is 0-75°.

[0041] A bending sensor of the utility model is tested for input and output response and recovery time. A square wave signal with a frequency of 1HZ and an amplitude of 2N is adjusted using a signal generator. The sensor is connected to the force transmission rod. The power amplifier is used to make the force transmission rod vibrate at this frequency. The sensor generates an output voltage signal. The square wave signal of any cycle is selected for analysis. The response time and recovery time in the waveform are 43ms and 46ms. When the applied force and frequency change, the response time and recovery time of the sensor do not change basically, which can meet the experimental requirements under various conditions.

[0042] Matters not covered in this utility model are known technologies.

Claims

1. A bending sensor based on a magnetic film, characterized by The sensor includes a magnetic film, a tunnel magnetoresistance sensor, and a flexible circuit board; wherein two tunnel magnetoresistance sensors are fixed on the flexible circuit board at intervals, and the magnetic film covers the flexible circuit board and wraps the tunnel magnetoresistance sensor therein; The magnetic film is a NdFeB-silicone elastomer composite film, the mass ratio of the two is 3:1; the film thickness is 1.7-1.85 mm; The distance between the two tunnel magnetoresistance sensors is 24 to 28 mm.

2. The bending sensor based on magnetic film according to claim 1, characterized in that the model of the tunnel magnetoresistance sensor is TMR2003, the magnetic sensitive direction is horizontal, the size is 3mm×3mm×1.45mm, and the package form is SOT23-5; The flexible circuit board is an FPC, and its size is 66mm×9mm×0.2mm.

3. The bending sensor based on the magnetic film as described in claim 1 is characterized in that the magnetic film is divided into five areas, and the directions of the magnetic fields in each area are upward, downward, upward, downward and upward from left to right.

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