A low-frequency capacitive closed-loop acceleration sensor

Abstract

The present invention discloses a low-frequency capacitive closed-loop acceleration sensor, which uses a multi-layer circuit board made of FR4 material as the main body of the low-frequency capacitive acceleration sensor. The main body circuit board includes: a mass block for detecting vibration; an elastic structure formed by CNC machining to form a folded cantilever beam; a coil structure in the middle layer of the circuit board and two groups of copper metal arrays on the top layer. A circuit board symmetric to the copper metal array is welded and fixed above the main body circuit board to form a differential capacitance plate. There is an acrylic shell with grooves outside, and a set of magnets with opposite magnetic fields in the vertical direction are placed at the left and right grooves respectively. Interfaces are left around the circuit board for introducing coil current, and combining with the magnetic field to generate Ampere force to achieve closed-loop control. The sensor of the present invention can detect low-frequency signals (<10Hz), has a simple production process, low material cost, and has good anti-interference and stability.

Description

Technical Field

[0001] The present invention relates to a low-frequency capacitive closed-loop acceleration sensor, belonging to the technical field of acceleration sensors. Background Art

[0002] Low-frequency vibrations are common in life. For example, the vibrations generated by a car driving on the road surface, the natural vibration frequency of a highway bridge, and the seismic signals generated during geological structure exploration in the engineering field. The vibration frequencies of these signals are generally below 100 Hz. Existing inertial sensors on the market are mainly designed for high-frequency signals. The signals generated by such low-frequency vibrations are mixed in the noise and cannot be extracted, making it difficult to achieve effective analysis. Currently, scholars at home and abroad attach great importance to the research on low-frequency signal measurement, and capacitive acceleration sensors are favored due to their strong anti-interference ability and high measurement accuracy. Therefore, a capacitive acceleration sensor using new materials and simplified processes is proposed here, which can effectively reduce production costs and improve the detection performance of low-frequency signals below 10 Hz. Summary of the Invention

[0003] Technical Problem: The present invention provides a low-frequency capacitive acceleration sensor, which improves the detection performance of low-frequency signals, reduces production costs and effectively simplifies the production process.

[0004] Technical Solution: A low-frequency capacitive closed-loop acceleration sensor based on FR4 material, the low-frequency capacitive acceleration sensor of FR4 material includes:

[0005] In the middle of the main circuit board (1) of the low-frequency capacitive acceleration sensor of FR4 material is a mass block (11) for detecting the main body. At the left and right ends of the mass block (11), there are two elastic structures (12, 13) of folded cantilever beams, which are used to generate deformation under the action of acceleration;

[0006] On the top layer of the mass block (11), two groups of parallel copper metal arrays (15, 16) are laid. The middle layer contains a coil structure (17), and there are four square pads (18, 19, 20, 21) on the outer frame (14) of the circuit board.

[0007] There is an inverted upper cover circuit board (2) directly above the mass block (11). Four square pads are distributed at the four corners (24, 25, 26, 27) around it, corresponding to the positions of the four pads (18, 19, 20, 21) on the outer frame (14) of the main circuit board (1). The pads are connected by soldering.

[0008] On the top layer of the upper cover circuit board (2), two groups of parallel copper metal arrays (22, 23) are laid. The phase of the metal array is half different from that of the copper metal arrays (15, 16) to form differential capacitive plates.

[0009] The metal arrays (22, 23) on the upper cover board circuit board (2) are connected to the square pads (24, 25) through copper wires.

[0010] In the above solution, there are 6 pads on the right side of the outer frame (14) of the main circuit board (1). The pads (18, 19) are connected to the pads (28, 29) through copper wires for leading out the sensor output carrier signal line; the pads (30, 31) are connected to the parallel copper metal arrays (15, 16) through copper wires to input differential high-frequency sine signals; the pads (32, 33) are connected to the bottom coil structure (17) of the mass block (11) through copper wires for the input of the coil current signal, and combined with the magnet to generate Ampere force to increase the sensor damping and enhance the stability of the sensor.

[0011] In the above solution, after the main circuit board (1) and the upper cover board circuit board (2) are fixed by soldering, they are placed in the groove (34) of the base (3). There are three small notches (35, 36, 37) around the base (3), and there are three protrusions (38, 39, 40) with the same position dimensions on the corresponding outer cover (4) to clamp and fix it on the base, forming protection for the main structure of the sensor.

[0012] In the above solution, the four magnets (5, 6, 8, 9) have the same size. There are two grooves (41, 42) inside the first groove container (7) for placing the magnets (5, 6), and their upward polarities are opposite. The structure of the second groove container (10) is the same as that of the first groove container (7), and there are two grooves (43, 44) inside for placing the magnets (8, 9), and their downward polarities are opposite. The magnet on the left has the S pole facing down and the N pole facing up, and the magnet on the right has the N pole facing down and the S pole facing up.

[0013] The motion of the present invention can be regarded as a mechanical system of a spring k, a damper c, and a mass m. The mechanical model of the system is:

[0014]

[0015] Where m is the mass of the sensitive part, c is the damping coefficient of the system, k is the elastic stiffness of the system, t is the response time of the system; x(t) is the displacement generated by the sensitive structure changing with time, and a(t) is the value of the external acceleration received by the system. mnd 2 x(t) / dt 2 It represents the stress caused by inertia when the accelerometer receives an external acceleration. c dx(t) / dt is the resistance received by the system, and kx(t) is the restoring force of the spring structure inside the accelerometer.

[0016] When the externally applied acceleration is a steady-state constant acceleration, the static sensitivity of the accelerometer can be obtained as Where ωn is the natural frequency of the system.

[0017] This acceleration sensor adopts a variable area detection method. When there is no external acceleration, the initial capacitance is

[0018]

[0019] where l0 is the length of the directly opposite part of the electrodes, w is the directly opposite width of the two electrodes, C1 and C2 are the capacitance values of the left and right capacitors, ε is the relative permittivity, ε0 is the vacuum permittivity, and d0 is the distance between the plates.

[0020] When acceleration is generated, the capacitance changes by ΔC

[0021]

[0022] where x is the offset generated by the plates.

[0023] The mechanical sensitivity of this sensor is

[0024]

[0025] The minimum resolution of this sensor is

[0026]

[0027] The present invention has the following beneficial effects:

[0028] 1. This low-frequency capacitive closed-loop acceleration sensor based on FR4 material provided by the present invention adopts an elastic structure of a folded cantilever beam, effectively improving the sensitivity of the sensor.

[0029] 2. This low-frequency capacitive closed-loop acceleration sensor based on FR4 material provided by the present invention uses the same material as the printed circuit board (PCB), which is easy to obtain, and its production process is compatible with the existing PCB process, with a relatively low cost.

[0030] 3. This low-frequency capacitive closed-loop acceleration sensor based on FR4 material provided by the present invention can be formed by a planar CNC cutting process for its elastic structure, simplifying the production process. Brief Description of the Drawings

[0031] Figure 1 is the front structural schematic diagram of the overall structure of the low-frequency capacitive closed-loop acceleration sensor based on FR4 material of the present invention;

[0032] Figure 2 is the top-layer structural schematic diagram of the main circuit board 1 of the low-frequency capacitive closed-loop acceleration sensor based on FR4 material of the present invention;

[0033] Figure 3Schematic diagram of the bottom layer structure of the main circuit board 1 of the low-frequency capacitive closed-loop acceleration sensor based on FR4 material of the present invention;

[0034] Figure 4 Schematic diagram of the structure of the upper cover board circuit board 2 in the low-frequency capacitive closed-loop acceleration sensor based on FR4 material of the present invention;

[0035] Figure 5 Schematic diagram of the structure of the base 3 in the low-frequency capacitive closed-loop acceleration sensor based on FR4 material of the present invention;

[0036] Figure 6 Schematic diagram of the structure of the upper cover 4 in the low-frequency capacitive closed-loop acceleration sensor based on FR4 material of the present invention;

[0037] Figure 7 Schematic diagram of the structures of the first groove container 7 and the second groove container 10 in the low-frequency capacitive closed-loop acceleration sensor based on FR4 material of the present invention. Detailed implementation manners

[0038] To make the objectives, technical solutions and advantages of the present invention described more clearly and understandably, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings.

[0039] The structural schematic diagram of the low-frequency capacitive closed-loop acceleration sensor based on FR4 material provided by the present invention is as Figure 1 shown. The main circuit board 1 of the low-frequency capacitive closed-loop acceleration sensor based on FR4 material, and the upper cover board circuit board 2 connected thereto by soldering, are placed on the base 3 and protected by the outer cover 4. There is a pair of magnets 5, 6 placed in a first groove container 7 under the base 3, and the same pair of magnets 8, 9 are placed in a second groove container 10 above the outer cover 4.

[0040] As Figure 2 shown, the main circuit board 1, as the main body of the low-frequency capacitive acceleration sensor made of FR4 material, forms an elastic structure 12, 13 with two folded cantilever beams at the left and right ends through planar engraving by a CNC engraving machine and is connected to the outer frame 14. In the middle of the main circuit board 1 is the mass block 11 for detecting the main body. On the top layer of the mass block 11, two groups of parallel copper metal arrays 15, 16 are laid. Four square pads 18, 19, 20, 21 on the circuit board outer frame 14 are used for bonding with the upper cover board circuit board 2. There are 6 pad ports on the right side of the outer frame 14 of the main circuit board 1. The pads 18, 19 are connected to the pads 28, 29 through copper wires for leading out the carrier signal line output by the sensor; the pads 30, 31 are connected to the parallel copper metal arrays 15, 16 through copper wires to input differential high-frequency sine signals.

[0041] As Figure 3As shown, a coil structure 17 is printed on the mass block at the bottom layer of the main circuit board 1. The coil structure 17 is a square planar coil made of copper wire, which is connected to the top layer pads 32 and 33 through vias. When an input current is applied, an Ampere force is generated in combination with the magnet to increase the sensor damping and enhance the stability of the sensor.

[0042] As Figure 4 shown, two groups of parallel copper metal arrays 22 and 23 are laid on the top layer of the upper cover circuit board 2. After bonding, they form a differential capacitance structure with the two groups of parallel copper metal arrays 15 and 16 on the mass block 11 of the main circuit board 1 with a half difference. There are four square pads distributed at the four corners 24, 25, 26, and 27 around, and the metal arrays 22 and 23 are connected to the square pads 24 and 25 through copper wires.

[0043] As Figure 5 shown, the base 3 has a shallow groove inside, with the size and depth consistent with the outer frame 14 of the circuit board, for placing the main circuit board 1 and the upper cover circuit board 2. Three notches 35, 36, and 37 are engraved around, which are formed by CNC milling.

[0044] As Figure 6 shown, the outer cover 4 has three protrusions 38, 39, and 40 with the same position dimensions for clamping and fixing it on the base 3 to form protection for the main structure of the sensor.

[0045] As Figure 7 shown, there are two grooves 41 and 42 facing upward inside the first groove container 7 for placing the magnets 5 and 6, with their upward polarities opposite. The structure of the second groove container 10 is the same as that of the first groove container 7, and there are two grooves 43 and 44 inside for placing the magnets 8 and 9, with their downward polarities opposite. The left group of magnets has the S pole facing down and the N pole facing up, and the right group of magnets has the N pole facing down and the S pole facing up.

[0046] The working principle of this low-frequency capacitive closed-loop acceleration sensor based on FR4 material provided by the present invention is as follows:

[0047] When an external vibration signal is generated, the mass block 11 on the main circuit board 1 and the elastic structures 12 and 13 of the folded cantilever beam form a mass-spring system. The mass block 11 vibrates horizontally in the X-axis direction of the sensor, resulting in a change in the area of the capacitance plates formed by the top copper metal arrays 15 and 16 and the parallel copper metal arrays 22 and 23 covered on the upper cover circuit board 2 above. The capacitance change is proportional to the displacement of the mass block 11, and the mass block displacement is proportional to the acceleration.

[0048] The pads 30 and 31 are connected by copper wires to the parallel copper metal arrays 15 and 16 to input differential high-frequency sine signals. The copper metal arrays 22 and 23 on the upper plate at the other end will carry a carrier signal. When subjected to external acceleration, the facing area of the two sets of differential capacitor plates will change, resulting in a change in the capacitance value. Therefore, the output carrier signal will also be affected and changed, and then sent to the subsequent circuit for processing and converted into an analog quantity.

[0049] The structure designed in the present invention can adjust and change its mechanical sensitivity, natural frequency, and background noise by means of the area of the copper metal or other metal arrays 15 and 16, the stiffness of the elastic structures 12 and 13 of the folding cantilever beams, or the distance parameter between the upper cover circuit board 2 and the mass block 11.

[0050] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and shall not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention shall be covered within the protection scope of the present invention.

Claims

1. A low-frequency capacitive closed-loop acceleration sensor, characterized in that, It includes a main circuit board (1), an upper cover circuit board (2), and an outer frame (14). In the middle of the main circuit board (1) is a mass (11) for detecting the main body. Elastic structures in the form of folded cantilever beams are respectively arranged at the left and right ends of the mass (11). The left and right ends of the elastic structures are respectively connected to the mass (11) and the outer frame (14). On the top layer of the mass (11), two groups of parallel copper metal arrays (15, 16) are laid. On the bottom layer of the mass (11), a coil structure (17) is printed. On the outer frame (14), there are four square pads (18, 19, 20, 21). On the top layer of the upper cover circuit board (2), two groups of parallel copper metal arrays (22, 23) are laid. Four square pads (24, 25, 26, 27) are distributed at the four corners around. Among them, the two groups of parallel copper metal arrays (22, 23) are connected to the square pads (24, 25) through copper wires. The two groups of parallel copper metal arrays (22, 23) laid on the top layer of the upper cover circuit board (2) and the two groups of parallel copper metal arrays (15, 16) laid on the top layer of the mass (11) differ by half to form differential capacitance plates.

2. The low-frequency capacitive closed-loop acceleration sensor according to claim 1, characterized in that The material of the main circuit board (1) is FR4 material.

3. The low-frequency capacitive closed-loop acceleration sensor according to claim 1, characterized in that, The elastic structure includes two groups of springs connected in series.

4. A low-frequency capacitive closed-loop acceleration sensor according to claim 1, characterized in that, The two elastic structures at the left and right ends are respectively two groups of springs connected in series. Between the top parts of the left ends and the top parts of the right ends, and between the bottom parts of the left ends and the bottom parts of the right ends of each group of springs, connection beams are used for connection.

5. A low-frequency capacitive closed-loop acceleration sensor according to claim 1, characterized in that, The main circuit board (1) and the upper cover circuit board (2) are placed on a base (3) and are protected by an outer cover (4). Under the base (3), a pair of magnets (5, 6) are placed in a first groove container (7). Above the outer cover (4), the same pair of magnets (8, 9) are placed in a second groove container (10).

6. The low-frequency capacitive closed-loop acceleration sensor according to claim 1, characterized in that, The upper cover circuit board (2) is placed upside down on the main circuit board (1). The four pads (24, 25, 26, 27) on the upper cover circuit board (2) and the four pads (18, 19, 20, 21) of the outer frame (14) of the main circuit board (1) are in one-to-one correspondence, and the corresponding pads are connected and fixed up and down by brazing.

7. The low-frequency capacitive closed-loop acceleration sensor according to claim 1, characterized in that, On the right side of the outer frame (14) of the main circuit board (1), there are 6 pad ports. The pads (18, 19) are connected to the pads (28, 29) through copper wires for leading out the sensor output carrier signal line; the pads (30, 31) are connected to the parallel copper metal arrays (15, 16) through copper wires to input differential high-frequency sine signals; the pads (32, 33) are connected to the internal coil structure (17) of the mass (11) for input of coil current signals.

8. The low-frequency capacitive closed-loop acceleration sensor according to claim 1, characterized in that, Inside the base (3), there is a groove (34) with the same planar size as the main circuit board (1) for placing the main circuit board (1) and the upper cover circuit board (2). There are three small notches (35, 36, 37) around the base (3). Corresponding to the outer cover (4), there are three protrusions (38, 39, 40) with the same position dimensions for clamping and fixing it on the base to form protection for the sensor main body structure.

9. The low-frequency capacitive closed-loop acceleration sensor according to claim 5, characterized in that, The four magnets (5, 6, 8, 9) are of the same size. Inside the first groove container (7), there are two grooves (41, 42) for placing the magnets (5, 6), and the polarities facing upward of the two are opposite; the second groove container (10) has the same structure as the first groove container (7), and inside there are two grooves (43, 44) for placing the magnets (8, 9), and the polarities facing downward of the two are opposite; the magnet on the left has its S-pole facing downward and N-pole facing upward, and the magnet on the right has its N-pole facing downward and S-pole facing upward.

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