CN203758458U - Optical fiber Bragg grating large displacement sensor based on gear rotary type - Google Patents

Abstract

The utility model relates to a large-displacement sensor based on a gear-rotating optical fiber Bragg grating, which belongs to the technical field of optoelectronic measurement. It includes a displacement measurement and transmission device, a displacement size conversion device and a displacement sensing device, and the above devices are fixed inside the metal box. The main body of the displacement measurement and transmission device is fixed in the metal box through the rack sleeve I and the rack sleeve II. The internal rack Ⅰ, the upper end of the rack Ⅰ extends out of the metal box and is fixed by a displacement limit sleeve; the structure of the displacement conversion device is a stepped shaft coaxially connecting the large gear and the pinion; this device can realize large displacement And real-time online monitoring of temperature.

Description

A large displacement sensor based on gear rotating fiber Bragg grating

technical field

The utility model relates to a large-displacement sensor based on a gear-rotating optical fiber Bragg grating, which belongs to the technical field of optoelectronic measurement.

Background technique

In recent years, accidents such as bridge collapses, tunnel collapses, and landslides along the way have occurred frequently in my country. Timely and accurate grasp of crack changes and relative position slippage in civil structures makes displacement detection particularly important. At present, the existing fiber grating displacement sensors generally fix the fiber grating on various elastic beams, convert the displacement to the strain of the grating through the deformation of the beam (shrapnel), and measure the corresponding displacement by demodulating the wavelength drift of the grating. This kind of sensor has high precision, anti-electromagnetic interference, stable chemical properties and can meet distributed measurement. The disadvantage is that the measuring range is small (generally less than 200mm), and it is difficult to package into a sensor suitable for engineering applications.

What is close to the present invention is a fiber grating displacement sensor (refer to literature: Li Lijun, "A Fiber Bragg Grating Displacement Sensor", Invention Patent Specification, June 2010, authorized announcement number: CN 101762247 A). This technology uses an angular displacement conversion device to measure external large displacements. Due to the multi-stage gears used in the angular displacement conversion device, measurement deviations are prone to occur and packaging is difficult. The utility model uses a stepped shaft to fix two gears with different radii on the same shaft, and transforms the large displacement of linear motion through the conversion of the two gears, and finally acts on the optical fiber Bragg grating pasted on the cantilever beam of equal strength, realizing Real-time online monitoring of large displacement and temperature.

Contents of the invention

The technical problem to be solved by the utility model is to provide a gear-rotating optical fiber Bragg grating large displacement sensor to realize real-time online monitoring of large displacement and temperature.

The structure of the sensor of the present utility model is as follows: it includes a displacement measurement and transmission device, a displacement size conversion device and a displacement induction device, and the above-mentioned devices are all fixed inside the metal box 17, and the main body of the displacement measurement and transmission device is through the rack sleeve I12 The rack I5 and the rack sleeve II13 are fixed inside the metal box 17, and the upper end of the rack I5 extends out of the metal box 17 and is fixed by the displacement limit sleeve 11; the structure of the displacement size conversion device is that the stepped shaft 10 is coaxial Connect the large gear 3 and the pinion 4; the main body of the displacement sensing device is a rack II6 which is fitted through the rack sleeve III14 at the upper end and fixedly connected with the cantilever beam 2 at the lower end. Fiber Bragg grating 1; rack I5 meshes with gear 3, rack II6 meshes with pinion 4.

The bottom end of the rack I5 is installed inside the metal box 17 through the spring I15, and the top end of the rack II6 is fixed in the metal box 17 through the spring II.

The two ends of the stepped shaft 10 are installed inside the metal box 17 through the rolling bearing I8 and the rolling bearing II9 respectively.

The fiber Bragg grating 1 is installed on the central axis of the upper and lower surfaces of the equal strength cantilever beam 2 .

The fiber Bragg grating 1 is pasted on the cantilever beam 2 of equal strength.

The usage method of the sensor of the utility model is to establish a mathematical model inside the sensor, through which the numerical value actually measured by the sensor can be converted to the Bragg wavelength shift of the optical fiber Bragg grating to calculate the displacement measured by the displacement sensor. The specific steps include the following:

(1) The strain displacement is measured by measuring the contact head 7, the large displacement of the rack I5 is coaxially converted into the small displacement of the pinion 4 through the large gear 3, and then the deformation of the cantilever beam 2 of equal strength is caused by the rack II6, and the equal strength The deformation of the cantilever beam causes the deformation of the fiber Bragg grating, and the wavelength shift of the fiber Bragg grating caused by the strain displacement and temperature is obtained for:

In the formula, is the strain sensitivity coefficient, the magnitude of which is ,in is the effective elastic-optical coefficient, and its value is =0.22, is the temperature sensitivity coefficient, is the central wavelength of the fiber Bragg grating, is the strain on the fiber Bragg grating, is the temperature variation of the fiber Bragg grating;

(2) Subtract the wavelength shifts of two fiber Bragg gratings with the same initial wavelength installed on the upper and lower surfaces of the equal-strength cantilever beam 2 to eliminate the influence of ambient temperature, and obtain the wavelength shift difference of the two fiber Bragg gratings on the upper and lower surfaces as :

In the formula, , are the wavelength shifts of the fiber Bragg grating on the upper and lower surfaces of the wave, respectively;

(3) According to the mechanics of materials, the central axial strain of the equal-strength cantilever beam caused by the deflection f of the equal-strength cantilever beam is obtained as:

According to the positional relationship between the gear and the rack in the sensor, the relationship between the Bragg wavelength shift of the fiber Bragg grating and the actual external displacement is obtained as follows:

In the formula, h is the thickness of the constant strength beam, is the length of the equal-strength beam, f is the deflection of the free end of the equal-strength cantilever beam, S is the displacement of the rack I5 (that is, the actual external displacement), is the radius of the bull gear 3, is the radius of pinion 4.

The mathematical model of the utility model technology is as follows:

The deformation of the equal-strength cantilever beam causes the deformation of the fiber Bragg grating, if the temperature changes during the measurement , then the wavelength shift of the fiber Bragg grating caused by strain and temperature for:

(1)

In formula (1), is the strain sensitivity coefficient, the magnitude of which is ,in is the effective elastic-optical coefficient, and its value is =0.22, is the temperature sensitivity coefficient, is the central wavelength of the fiber Bragg grating, is the strain on the fiber Bragg grating, is the temperature variation of the fiber Bragg grating.

Subtract the wavelength shift of two fiber Bragg gratings with the same initial wavelength pasted on the upper and lower surfaces of the equal-strength cantilever to eliminate the influence of the ambient temperature:

(2)

In formula (2), is the wavelength shift difference of the two fiber Bragg gratings on the upper and lower surfaces, , are the wavelength shifts of the fiber Bragg grating on the upper and lower surfaces of the wave, respectively.

According to the calculation formula of material mechanics, the central axial strain of the equal-strength cantilever beam caused by the deflection f of the equal-strength cantilever beam is:

(3)

In formula (3), h is the thickness of the equal strength beam, is the equal strength beam length.

Since the deflection f of the free end of the equal-strength cantilever beam is generally small, the displacement of the rack II6 acting on the free end of the equal-strength cantilever beam is f, so the number of teeth rotated by pinion 4 is:

(4)

In formula (4), is the radius of pinion 4, 4 teeth for the pinion.

The rotation angle of pinion 4 is:

(5)

In formula (5), is the radius of pinion 4.

The small gear 4 and the large gear 3 rotate coaxially, so the angle through which the large gear 3 turns is , so the number of teeth that the big gear 3 has rotated is:

(6)

In formula (6), It is the number of teeth of the large gear with 3 teeth.

From this, the displacement of the rack I5 can be obtained as:

(7)

In formula (7), is the radius of the bull gear 3, and the displacement S of the rack I5 is the actual external displacement.

From formula (6) can get:

(8)

Substituting equation (8) into equation (2), the strain on the cantilever beam The relationship with the external actual displacement is:

(9)

Substituting (9) into (1), the relationship between the Bragg wavelength shift of the fiber Bragg grating and the actual external displacement is:

(10)

Equation (10) shows the mathematical model between the displacement S measured by the displacement sensor and the Bragg wavelength shift of the fiber Bragg grating. The displacement measured by the displacement sensor can be calculated by measuring the Bragg wavelength shift of the fiber Bragg grating.

The beneficial effects of the utility model are:

(1) Large measuring range. Due to the adoption of a double-gear displacement conversion structure, the external large displacement is converted into a small displacement to be measured by the sensor.

(2) High sensitivity. Due to the simple structure of the displacement sensor, high-sensitivity measurement can be realized by adjusting the radius ratio of gear 3 and gear 4 .

(3) Realize on-line monitoring of displacement: Rack 6 acts on the equal-strength cantilever beam with the small displacement converted by the displacement conversion device of gear 3 and gear 4, so that the deflection of the equal-strength cantilever beam changes, resulting in sticking on the equal-strength cantilever beam. The Bragg wavelength of the fiber Bragg grating on the central axis of the upper and lower surfaces of the strength cantilever beam is shifted, and the size of the external displacement can be calculated by measuring the wavelength change of the fiber Bragg grating.

Description of drawings

Fig. 1 is the structural representation of the utility model;

Fig. 2 is a structural schematic diagram of a rolling bearing and a stepped shaft of the present invention.

The labels in the figure represent in turn: 1-fiber Bragg grating, 2-equal strength cantilever beam, 3-big gear, 4-pinion, 5-rack I, 6-rack II, 7-measuring contact head, 8- Rolling bearing Ⅰ, 9-rolling bearing Ⅱ, 10-step shaft, 11-displacement limit sleeve, 12-rack sleeve Ⅰ, 13-rack sleeve Ⅱ, 14-rack sleeve Ⅲ, 15-spring Ⅰ, 16-spring II, 17-metal box, 18-external optical fiber.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment, the utility model is described further.

Embodiment 1: As shown in Figures 1 and 2, this embodiment is based on the structure of a gear-rotating fiber Bragg grating large displacement sensor: it includes a displacement measurement and transmission device, a displacement size conversion device and a displacement sensing device, and the above devices are fixed on Inside the metal box 17, the main body of the displacement measurement and transmission device is the rack I5 fixed inside the metal box 17 through the rack sleeve I12 and the rack sleeve II13. The upper end of the rack I5 extends out of the metal box 17 and passes through the displacement The limit sleeve 11 is fixed; the structure of the displacement conversion device is that the stepped shaft 10 is coaxially connected to the large gear 3 and the pinion 4; the main body of the displacement sensing device is through the upper end through the rack sleeve III 14 fit, and the lower end through the equal-strength cantilever The beam 2 is fixedly connected to the rack II6, and the upper and lower surfaces of the equal-strength cantilever beam 2 are equipped with a fiber Bragg grating 1; the rack I5 meshes with the large gear 3, and the rack II6 meshes with the pinion 4. The bottom end of the rack I5 is installed inside the metal box 17 through the spring I15, and the top end of the rack II6 is fixed in the metal box 17 through the spring II. The two ends of the stepped shaft 10 are installed inside the metal box 17 through the rolling bearing I8 and the rolling bearing II9 respectively. The fiber Bragg grating 1 is installed on the central axis of the upper and lower surfaces of the equal-strength cantilever beam 2 . The fiber grating 1 is installed on the cantilever beam 2 of equal strength by sticking.

The method of using the sensor in this embodiment is to establish a mathematical model inside the sensor, through which the value actually measured by the sensor can be converted to the Bragg wavelength shift of the fiber Bragg grating to calculate the displacement measured by the displacement sensor. The specific steps include the following:

(1) The strain displacement is measured by measuring the contact head 7, the large displacement of the rack I5 is coaxially converted into the small displacement of the pinion 4 through the large gear 3, and then the deformation of the cantilever beam 2 of equal strength is caused by the rack II6, and the equal strength The deformation of the cantilever beam causes the deformation of the fiber Bragg grating, and the wavelength shift of the fiber Bragg grating caused by the strain displacement and temperature is obtained for:

In the formula, is the strain sensitivity coefficient, the magnitude of which is ,in is the effective elastic-optical coefficient, and its value is =0.22, is the temperature sensitivity coefficient, is the central wavelength of the fiber Bragg grating, is the strain on the fiber Bragg grating, is the temperature variation of the fiber Bragg grating;

(2) Subtract the wavelength shifts of two fiber Bragg gratings with the same initial wavelength installed on the upper and lower surfaces of the equal-strength cantilever beam 2 to eliminate the influence of ambient temperature, and obtain the wavelength shift difference of the two fiber Bragg gratings on the upper and lower surfaces as :

In the formula, , are the wavelength shifts of the fiber Bragg grating on the upper and lower surfaces of the wave, respectively;

(3) According to the mechanics of materials, the central axial strain of the equal-strength cantilever beam caused by the deflection f of the equal-strength cantilever beam is obtained as:

According to the positional relationship between the gear and the rack in the sensor, the relationship between the Bragg wavelength shift of the fiber Bragg grating and the actual external displacement is obtained as follows:

In the formula, h is the thickness of the constant strength beam, is the length of the equal-strength beam, f is the deflection of the free end of the equal-strength cantilever beam, S is the displacement of the rack I5 (that is, the actual external displacement), is the radius of the bull gear 3, is the radius of pinion 4.

The specific parameters of this embodiment are: cantilever beam size: length l=200mm, thickness h=2mm; gear size: gear 1 radius =150mm, gear 2 radius =25mm; fiber Bragg grating technical parameters: central wavelength =1547.000nm, effective elastic-optical coefficient =0.22; use a fiber grating analyzer to obtain the Bragg wavelength of the fiber Bragg grating; according to the following formula, the response sensitivity of the Bragg wavelength shift of the fiber Bragg grating to the displacement is:

Substituting the known quantity into the formula, theoretical calculation shows that the sensitivity of the displacement sensor is 20.11pm/mm. Therefore, when the wavelength resolution of the fiber Bragg grating demodulator is 1pm, the resolution of the sensor is 0.0497mm. The calculation results show that the measuring range of the sensor is close to 300mm, and it has high measurement resolution and small measurement error.

Embodiment 2: As shown in Figures 1 and 2, this embodiment is based on the structure of a gear-rotating optical fiber Bragg grating large-displacement sensor: it includes a displacement measurement and transmission device, a displacement size conversion device and a displacement sensing device, and the above-mentioned devices are all fixed on the Inside the metal box 17, the main body of the displacement measurement and transmission device is the rack I5 fixed inside the metal box 17 through the rack sleeve I12 and the rack sleeve II13. The upper end of the rack I5 extends out of the metal box 17 and passes through the displacement The limit sleeve 11 is fixed; the structure of the displacement conversion device is that the stepped shaft 10 is coaxially connected to the large gear 3 and the pinion 4; the main body of the displacement sensing device is through the upper end through the rack sleeve III 14 fit, and the lower end through the equal-strength cantilever The beam 2 is fixedly connected to the rack II6, and the upper and lower surfaces of the equal-strength cantilever beam 2 are equipped with a fiber Bragg grating 1; the rack I5 meshes with the large gear 3, and the rack II6 meshes with the pinion 4. The bottom end of the rack I5 is installed inside the metal box 17 through the spring I15, and the top end of the rack II6 is fixed in the metal box 17 through the spring II. The two ends of the stepped shaft 10 are installed inside the metal box 17 through the rolling bearing I8 and the rolling bearing II9 respectively.

The method of using the sensor in this embodiment is to establish a mathematical model inside the sensor, through which the value actually measured by the sensor can be converted to the Bragg wavelength shift of the fiber Bragg grating to calculate the displacement measured by the displacement sensor. The specific steps include the following:

(1) The strain displacement is measured by measuring the contact head 7, the large displacement of the rack I5 is coaxially converted into the small displacement of the pinion 4 through the large gear 3, and then the deformation of the cantilever beam 2 of equal strength is caused by the rack II6, and the equal strength The deformation of the cantilever beam causes the deformation of the fiber Bragg grating, and the wavelength shift of the fiber Bragg grating caused by the strain displacement and temperature is obtained for:

In the formula, is the strain sensitivity coefficient, the magnitude of which is ,in is the effective elastic-optical coefficient, and its value is =0.22, is the temperature sensitivity coefficient, is the central wavelength of the fiber Bragg grating, is the strain on the fiber Bragg grating, is the temperature variation of the fiber Bragg grating;

(2) Subtract the wavelength shifts of two fiber Bragg gratings with the same initial wavelength installed on the upper and lower surfaces of the equal-strength cantilever beam 2 to eliminate the influence of ambient temperature, and obtain the wavelength shift difference of the two fiber Bragg gratings on the upper and lower surfaces as :

In the formula, , are the wavelength shifts of the fiber Bragg grating on the upper and lower surfaces of the wave, respectively;

(3) According to the mechanics of materials, the central axial strain of the equal-strength cantilever beam caused by the deflection f of the equal-strength cantilever beam is obtained as:

According to the positional relationship between the gear and the rack in the sensor, the relationship between the Bragg wavelength shift of the fiber Bragg grating and the actual external displacement is obtained as follows:

In the formula, h is the thickness of the constant strength beam, is the length of the equal-strength beam, f is the deflection of the free end of the equal-strength cantilever beam, S is the displacement of the rack I5 (that is, the actual external displacement), is the radius of the bull gear 3, is the radius of pinion 4.

The specific implementation of the utility model has been described in detail above in conjunction with the accompanying drawings, but the utility model is not limited to the above-mentioned implementation. Various changes are made.

Claims (5)

1. one kind based on the rotary optical fiber Bragg raster large displacement sensor of gear, it is characterized in that: comprise displacement measurement and transfer device, displacement size conversion device and displacement induction installation, and said apparatus is all fixed on can (17) inside, the main body of displacement measurement and transfer device is to be fixed on the inner tooth bar I (5) of can (17) by tooth bar sleeve pipe I (12) and tooth bar sleeve pipe II (13), and it is outside and fixing by displacement position-limiting sleeve pipe (11) that can (17) is stretched out in the upper end of tooth bar I (5); The structure of displacement size conversion device is that multidiameter (10) coaxially connects gear wheel (3) and pinion wheel (4); The main body of displacement induction installation is that the tooth bar II (6) that tooth bar sleeve pipe III (14) fit, lower end are fixedly connected with by equi intensity cantilever (2) is passed through in upper end, and the upper and lower surface of equi intensity cantilever (2) is provided with optical fiber Bragg raster (1); Tooth bar I (5) and gear wheel (3) engagement, tooth bar II (6) and pinion wheel (4) engagement.

2. according to claim 1 based on the rotary optical fiber Bragg raster large displacement sensor of gear, it is characterized in that: described tooth bar I (5) bottom is arranged on can (17) inside by spring I (15), and the top of tooth bar II (6) is fixed in can (17) by spring II.

3. according to claim 1 based on the rotary optical fiber Bragg raster large displacement sensor of gear, it is characterized in that: the two ends of described multidiameter (10) are arranged on can (17) inside by rolling bearing I (8) and rolling bearing II (9) respectively.

4. according to claim 1 based on the rotary optical fiber Bragg raster large displacement sensor of gear, it is characterized in that: described optical fiber Bragg raster (1) is arranged on the upper and lower surface central axis place of equi intensity cantilever (2).

5. according to claim 4 based on the rotary optical fiber Bragg raster large displacement sensor of gear, it is characterized in that: described optical fiber Bragg raster (1) is pasted on equi intensity cantilever (2).