Pressure sensor

Abstract

The invention discloses a pressure sensor. The pressure sensor comprises a pressure detection circuit and a resistance compensation device, wherein the pressure detection circuit comprises a Wheatstone bridge, and each bridge arm of the Wheatstone bridge is provided with one or more strain gauges; the pressure detection circuit is used for detecting force and / or torque in one or more directions; each strain gauge included in the circuit is provided with a corresponding resistance compensation device, and the resistance compensation devices are used for compensating the resistance values of the strain gauges generated along with the temperature change of the environment where the strain gauges are located in real time, so that the resistance values of the bridge arms where the strain gauges are located are kept constant. According to the pressure sensor provided by the embodiment of the invention, each strain gauge is provided with one corresponding resistance compensation device, and the resistance compensation devices compensate the resistance value generated by each strain gauge along with the temperature change of the environment where the strain gauge is located in real time, so that the pressure sensor can be randomly placed in an occasion with a temperature gradient; and the measurement precision and stability of the sensor are improved.

Description

Technical Field

[0001] This application relates to the technical field of sensors, and in particular, to a pressure sensor. Background Art

[0002] Temperature drift is a common problem affecting the accuracy of pressure sensors. When the temperature changes, the materials inside the pressure sensor expand or contract, causing changes in the structure of the pressure sensor, resulting in changes in the output sensitivity. Temperature changes also affect the performance of internal circuit elements of the pressure sensor, such as resistors and capacitors, further affecting the output results of the pressure sensor. When multiple strain gauges in the pressure sensor are at different temperatures due to differences in position or heat dissipation conditions, traditional strain gauge temperature compensation methods cannot accurately match and compensate for the changes in the resistance values of each strain gauge, resulting in large errors in temperature compensation and limiting the use of high-precision force sensors in complex temperature environments. Summary of the Invention

[0003] To solve the related technical problems, an embodiment of this application provides a pressure sensor.

[0004] The technical solution of the embodiment of this application is implemented as follows:

[0005] An embodiment of this application provides a pressure sensor, which includes: a pressure detection circuit and a resistance compensation device; wherein,

[0006] The pressure detection circuit includes a Wheatstone bridge, and one or more strain gauges are arranged on each arm of the Wheatstone bridge; the pressure detection circuit is used to detect force and / or torque in one or more directions;

[0007] Each strain gauge included in the pressure detection circuit is provided with a corresponding resistance compensation device, and the resistance compensation device is used to compensate in real time for the resistance value of the strain gauge generated as the temperature of the environment where the strain gauge is located changes, so that the resistance value of the arm where the strain gauge is located remains constant.

[0008] In some embodiments, the resistance compensation device includes a negative temperature coefficient (NTC) temperature sensor, and the NTC temperature sensor is arranged on the arm where the corresponding strain gauge is located and is connected in series with the corresponding strain gauge.

[0009] In some embodiments, when one strain gauge is arranged on each arm of the Wheatstone bridge, a first distance is less than a second distance. The first distance includes the distance between the NTC temperature sensor and the strain gauge on the same arm where the NTC temperature sensor is located; the second distance includes the distance between the NTC temperature sensor and the strain gauges on other arms outside the arm where the NTC temperature sensor is located.

[0010] In some embodiments, when at least two strain gauges are provided on each arm of the Wheatstone bridge, for each strain gauge, a third distance is less than a fourth distance, the third distance is less than a fifth distance, and the third distance includes the distance between the strain gauge and the corresponding first NTC temperature sensor; the fourth distance includes the distance between the first NTC temperature sensor and other strain gauges other than the strain gauge corresponding to the first NTC temperature sensor on the same arm, and the fifth distance includes the distance between the first NTC temperature sensor and the strain gauges on other arms other than the arm where the first NTC temperature sensor is located.

[0011] In some embodiments, the resistance compensation device further includes a temperature compensation resistor, which is connected in parallel with the NTC temperature sensor. The temperature compensation resistor and the NTC temperature sensor are used to compensate in real time for the resistance value change of the strain gauge due to the change of the ambient temperature where the strain gauge is located, so as to keep the resistance value of the arm where the strain gauge is located constant.

[0012] In some embodiments, the temperature compensation resistor includes a chip resistor.

[0013] In some embodiments, the resistance value of the chip resistor is related to the resistance value of the strain gauge corresponding to the chip resistor in the ambient environment and the resistance value of the NTC temperature sensor corresponding to the chip resistor in the ambient environment.

[0014] In some embodiments, the strain gauge includes a silicon strain gauge.

[0015] In some embodiments, for each arm of the Wheatstone bridge, the strain gauges and the resistance compensation devices on the arm are arranged on a first printed circuit board (Printed Circuit Board, PCB); all the first PCBs are arranged on a second PCB.

[0016] In some embodiments, the first PCB includes a flexible printed circuit (Flexible Printed Circuit, FPC).

[0017] The pressure sensor provided by the embodiment of the present application includes: a pressure detection circuit and a resistance compensation device; wherein, the pressure detection circuit includes a Wheatstone bridge, and one or more strain gauges are arranged on each arm of the Wheatstone bridge; the pressure detection circuit is used to detect force and / or torque in one or more directions; each strain gauge included in the pressure detection circuit is provided with a corresponding resistance compensation device, and the resistance compensation device is used to compensate in real time the resistance value generated by the strain gauge with the change of the ambient temperature where the strain gauge is located, so as to keep the resistance value of the arm where the strain gauge is located constant. In the pressure sensor provided by the embodiment of the present application, each strain gauge in the Wheatstone bridge is provided with a corresponding resistance compensation device, forming a sub-unit composed of the strain gauge and the resistance compensation device. In each sub-unit, the temperature drift direction of the resistance compensation device is opposite to that of the strain gauge. In this way, when the pressure sensor is in a variable temperature environment or each strain gauge is at a different temperature, in each sub-unit, the change amount of the resistance values of the strain gauge and the resistance compensation device is offset in real time, making each sub-unit equivalent to an ideal element not affected by temperature in the bridge, so that the resistance value of the arm where the sub-unit is located remains unchanged. Therefore, when the pressure sensor is in a variable temperature environment or multiple strain gauges are at different temperatures, the stable zero output voltage of the bridge can still be ensured. Therefore, the pressure sensor provided by the embodiment of the present application can accurately sense and compensate in real time the resistance value generated by each strain gauge with the change of the ambient temperature where the strain gauge is located, eliminate the influence of the temperature drift of the strain gauge on each arm of the bridge, enable the pressure sensor to be placed arbitrarily in a place with a temperature gradient, and improve the measurement accuracy and stability of the sensor. Description of the Drawings

[0018] Figure 1 It is a schematic circuit structure diagram of a pressure sensor provided by the embodiment of the present application;

[0019] Figure 2 It is a schematic circuit structure diagram included in another pressure sensor provided by the embodiment of the present application;

[0020] Figure 3 It is a schematic circuit structure diagram of a resistance compensation device provided by the embodiment of the present application;

[0021] Figure 4 It is a schematic circuit structure diagram of a six-axis force sensor provided by the application example of the present application;

[0022] Figure 5 It is a schematic structure diagram of a six-axis force sensor provided by the application example of the present application. Detailed Embodiment

[0023] The present application will be further described in detail below with reference to the drawings and embodiments.

[0024] It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] Before describing the embodiments of the present application, relevant terms are explained first.

[0026] Temperature drift refers to the change in the performance of electronic components and the physical properties of materials with temperature change, which is a common problem affecting the accuracy of pressure sensors. When the ambient temperature of the pressure sensor changes, the performance of the internal electronic components of the pressure sensor (such as the resistance value of the strain gauge) changes with temperature, affecting the measurement accuracy of the sensor; at the same time, the change in the ambient temperature of the pressure sensor will also cause the expansion or contraction of the pressure sensor material (such as the elastomer), resulting in mechanical structure deformation and further affecting the measurement accuracy of the sensor. Among them, the elastomer is one of the core components of the pressure sensor and is responsible for sensing external forces. When an external force acts on the elastomer, the elastomer will deform, and after the external force is removed, the elastomer can return to its original state; the strain gauge is fixed on the surface of the elastomer by pasting or embedding. When the elastomer deforms, the strain gauge will also deform accordingly, thereby changing the resistance value of the strain gauge. The change in the resistance value of the strain gauge is usually converted into a voltage signal through a Wheatstone bridge circuit, thereby outputting a measurable electrical signal.

[0027] Temperature gradient refers to the phenomenon of temperature difference existing between different positions or different objects. Specifically, each strain gauge is at a different temperature, and at this time, there is a temperature difference between different strain gauges, which is called a temperature gradient exists between each strain gauge.

[0028] In related technologies, during the design process of some pressure sensors, although the influence of temperature on strain gauges is considered, the adopted compensation method is relatively complex or the compensation effect is not ideal. For example, a temperature compensation circuit is set outside the bridge. In this temperature compensation method, since the temperature compensation circuit is set outside the bridge, only global compensation can be performed using this temperature compensation circuit. Therefore, it is necessary to use this temperature compensation circuit for temperature compensation only after the temperature field where the pressure sensor is located is stable to ensure the accuracy of the compensation result. That is to say, the above compensation method cannot perform real-time temperature compensation in a complex temperature environment. Specifically, in the above compensation method, the situation where the pressure sensor is in a variable temperature environment or there is a temperature gradient among the strain gauges is not considered. If the pressure sensor is in a variable temperature environment, when using the above temperature compensation circuit, the accurate global temperature cannot be determined in time, resulting in a lag in adjustment behind the actual temperature change during temperature compensation, making it difficult to perform temperature compensation in time. If multiple strain gauges in the pressure sensor are at different temperatures due to differences in position or heat dissipation conditions, that is, there is a temperature gradient among the strain gauges, when using the above temperature compensation circuit, after the resistance values of each bridge arm have changed, temperature compensation is performed based on the global temperature of the sensor. At this time, there are differences in the actual temperatures of the strain gauges, resulting in insufficient or excessive temperature compensation for some strain gauges in global compensation, exacerbating the imbalance of the bridge and increasing the output signal error.

[0029] Therefore, the above temperature compensation method limits the use of high-precision pressure sensors in complex temperature environments.

[0030] Based on this, in various embodiments of the present application, one or more strain gauges are provided on each arm of the Wheatstone bridge; the pressure detection circuit is used to detect force and / or torque in one or more directions; each strain gauge included in the pressure detection circuit is provided with a corresponding resistance compensation device, and the resistance compensation device is used to compensate in real time the resistance value generated by the strain gauge due to the change in the ambient temperature where the strain gauge is located, so as to keep the resistance value of the arm where the strain gauge is located constant. For the pressure sensor provided by the embodiments of the present application, each strain gauge in the Wheatstone bridge is provided with a corresponding resistance compensation device, forming a sub-unit composed of the strain gauge and the resistance compensation device. In each sub-unit, the temperature drift direction of the resistance compensation device is opposite to that of the strain gauge. In this way, when the pressure sensor is in a variable temperature environment or each strain gauge is at a different temperature, in each sub-unit, the change amount of the resistance values of the strain gauge and the resistance compensation device is offset in real time, making each sub-unit equivalent to an ideal element not affected by temperature in the bridge, so that the resistance value of the arm where the sub-unit is located remains unchanged. Therefore, when the pressure sensor is in a variable temperature environment or multiple strain gauges are at different temperatures, the stable zero output voltage of the bridge can still be ensured. Therefore, the pressure sensor provided by the embodiments of the present application can accurately sense and compensate in real time the resistance value generated by each strain gauge due to the change in the ambient temperature where the strain gauge is located, eliminate the influence of the temperature drift of the strain gauge on each arm of the bridge, enable the pressure sensor to be placed arbitrarily in a place with a temperature gradient, and improve the measurement accuracy and stability of the sensor.

[0031] An embodiment of the present application provides a pressure sensor, Figure 1 which is a schematic diagram of the circuit structure of a pressure sensor provided by an embodiment of the present application, as Figure 1 shown. The pressure sensor includes: a pressure detection circuit and a resistance compensation device 102; wherein,

[0032] The pressure detection circuit includes a Wheatstone bridge, and one strain gauge 101 is provided on each arm of the Wheatstone bridge; the pressure detection circuit is used to detect force and / or torque in one or more directions;

[0033] Each strain gauge 101 included in the pressure detection circuit is provided with a corresponding resistance compensation device 102, and the resistance compensation device 102 is used to compensate in real time the resistance value generated by the strain gauge 101 due to the change in the ambient temperature where the strain gauge 101 is located, so as to keep the resistance value of the arm where the strain gauge 101 is located constant.

[0034] Figure 2 which is a schematic diagram of the circuit structure included in another pressure sensor provided by an embodiment of the present application, as Figure 2 shown. The pressure sensor includes:

[0035] A pressure detection circuit and a resistance compensation device 102; wherein, the pressure detection circuit includes a Wheatstone bridge, and two strain gauges 101 are arranged on each arm of the Wheatstone bridge; the pressure detection circuit is used to detect force and / or torque in one or more directions;

[0036] Each strain gauge 101 included in the pressure detection circuit is provided with a corresponding resistance compensation device 102, and the resistance compensation device 102 is used to compensate in real time the resistance value of the strain gauge 101 generated due to the change of the ambient temperature where the strain gauge 101 is located, so that the resistance value of the arm where the strain gauge 101 is located remains constant.

[0037] Of course, in actual application, more strain gauges can be arranged on each arm.

[0038] As can be seen from the above description, the pressure sensor provided by the embodiment of the present application includes a pressure detection circuit and a resistance compensation device; wherein,

[0039] The pressure detection circuit includes a Wheatstone bridge, and one or more strain gauges are arranged on each arm of the Wheatstone bridge; the pressure detection circuit is used to detect force and / or torque in one or more directions; each strain gauge included in the pressure detection circuit is provided with a corresponding resistance compensation device, and the resistance compensation device is used to compensate in real time the resistance value of the strain gauge generated due to the change of the ambient temperature where the strain gauge is located, so that the resistance value of the arm where the strain gauge is located remains constant.

[0040] Wherein, in actual application, the time interval of the real-time compensation can be less than or equal to 0.1 second, and can be specifically determined according to the response time of the resistance compensation device; exemplarily, when the response time of the resistance compensation device from temperature change to resistance value change is 0.1 second, the time interval of the real-time compensation is also 0.1 second; at this time, every 0.1 second, the resistance compensation device will correspondingly change its own resistance value to compensate the resistance value of the strain gauge generated due to the change of the ambient temperature where the strain gauge is located, so that the resistance value of the arm where the strain gauge is located remains constant.

[0041] The resistance value of the arm where the strain gauge is located remains constant, that is, the resistance value of the arm where the strain gauge is located remains unchanged at the set value. In actual application, whenever the ambient temperature of the pressure sensor changes by 10 degrees Celsius, the change amount of the resistance value of the arm where the strain gauge is located within 5‰ (i.e., five-thousandths) of the set value can be regarded as the resistance value of the arm where the strain gauge is located remaining constant.

[0042] Figure 3 It is a schematic circuit diagram of a resistance compensation device 102 provided by the embodiment of the present application. From Figure 1 , Figure 2 And Figure 3As can be seen, the resistance compensation device 102 includes an NTC temperature sensor 1021. Each strain gauge 101 is provided with a corresponding NTC temperature sensor 1021, and the NTC temperature sensor 1021 is connected in series with the corresponding strain gauge 101.

[0043] As can be seen from the above description, for the pressure sensor provided in the embodiment of the present application, the resistance compensation device may include an NTC temperature sensor. The NTC temperature sensor is disposed on the bridge arm where the corresponding strain gauge is located and is connected in series with the corresponding strain gauge. Here, when the ambient temperature changes, the change in the resistance value of the NTC temperature sensor 1021 connected in series with the strain gauge 101 on the same bridge arm can correspondingly offset the change in the resistance value of the strain gauge 101, thereby achieving precise compensation for the resistance value of the strain gauge 101. Exemplarily, when the ambient temperature changes, if the resistance of the strain gauge 101 increases by 20 ohms, at this time, the resistance of the NTC temperature sensor 1021 correspondingly decreases by 20 ohms, and the change amounts of the two directly cancel each other out, so that the overall resistance value of the bridge arm where they are located is not affected. Therefore, even if multiple strain gauges are at different temperatures, a stable zero output voltage of the Wheatstone bridge can be ensured.

[0044] Here, in practical applications, the method for selecting the model of the NTC temperature sensor 1021 includes: determining the temperature drift characteristic of the strain gauge 101, that is, the relationship between the resistance value of the strain gauge 101 and temperature; determining the temperature drift characteristic of the NTC temperature sensor 1021 according to the temperature drift characteristic of the strain gauge 101, and selecting the parameters of the NTC temperature sensor 1021 according to the temperature drift characteristic of the NTC temperature sensor 1021, so as to determine the model of the NTC temperature sensor 1021, so that the change amounts of the resistances of the strain gauge 101 and the NTC temperature sensor 1021 can cancel each other out when the temperature changes;

[0045] The operating temperature range of the NTC temperature sensor 1021 should cover the operating temperature range of the strain gauge 101 to ensure that the resistance change of the strain gauge 101 can be effectively compensated throughout the temperature range. The temperature drift characteristic is also the change relationship of the resistance value with temperature, and can also be called the resistance temperature characteristic. The embodiment of the present application does not limit the name of the change relationship of the resistance value with temperature.

[0046] In practical applications, the expansion or contraction of the elastic body caused by the change in the ambient temperature where the pressure sensor is located will further affect the measurement accuracy of the sensor. At this time, the method for selecting the model of the NTC temperature sensor 1021 can include: determining the temperature drift characteristic of the strain gauge 101 provided on the elastic body, determining the temperature drift characteristic of the NTC temperature sensor 1021 according to the temperature drift characteristic of the strain gauge 101 provided on the elastic body, selecting the parameters of the NTC temperature sensor 1021 according to the temperature drift characteristic of the NTC temperature sensor 1021, so as to determine the model of the NTC temperature sensor 1021, so that the change in resistance of the strain gauge 101 provided on the elastic body and the NTC temperature sensor 1021 can cancel each other out when the temperature changes.

[0047] When the NTC temperature sensor 1021 is relatively close to the strain gauge 101 on the same bridge arm, it can more quickly and accurately sense the temperature change of the local environment where the strain gauge 101 corresponding to the NTC temperature sensor 1021 is located, so as to perform resistance compensation more timely.

[0048] Based on this, in some embodiments, when a strain gauge 101 is provided on each bridge arm of the Wheatstone bridge, the first distance is less than the second distance. The first distance includes the distance between the NTC temperature sensor 1021 and the strain gauge 101 on the same bridge arm where the NTC temperature sensor is located; the second distance includes the distance between the NTC temperature sensor 1021 and the strain gauge 101 on other bridge arms outside the bridge arm where the NTC temperature sensor 1021 is located.

[0049] Here, in practical applications, the calculation method of the distance can include: determining the geometric centers of the NTC temperature sensor 1021 and the strain gauge 101 on the pressure sensor, and then connecting the geometric centers of the NTC temperature sensor 1021 and the strain gauge 101 with a straight line segment to obtain the length of the straight line segment from the geometric center of the NTC temperature sensor 1021 to the geometric center of the strain gauge 101. The length of the straight line segment is the distance between the NTC temperature sensor 1021 and the strain gauge 101.

[0050] The calculation method of the distance can also include: determining the geometric centers of the regions where the resistance values of the NTC temperature sensor 1021 and the strain gauge 101 are sensitive to temperature changes, and then connecting the geometric centers of the regions where the resistance values of the NTC temperature sensor 1021 and the strain gauge 101 are sensitive to temperature changes with a straight line segment to obtain the length of the straight line segment. The length of the straight line segment is the distance between the NTC temperature sensor 1021 and the strain gauge 101.

[0051] The calculation method of the distance may also include: determining two points on the outer contours of the NTC temperature sensor 1021 and the strain gauge 101 that are closest to each other, and then connecting the two points with a straight line segment, and the length of the straight line segment is the distance between the NTC temperature sensor 1021 and the strain gauge 101. It can be understood that the setting of the distance can achieve the expected temperature compensation effect of the NTC temperature sensor 1021 on the corresponding strain gauge 101, and the embodiments of the present application do not limit the determination method of the distance.

[0052] Among them, the geometric center includes the center point symmetrically distributed in each direction of the object; for example, when the strain gauge 101 is a regular rectangle, the geometric center is located at the intersection of the two diagonals of the strain gauge 101; when the electronic component is an irregular shape, the electronic component is divided into multiple regular shapes, and the area and geometric center position of each regular shape are calculated, and the weighted average method is used to calculate the overall geometric center. The embodiments of the present application do not limit the determination method of the geometric center.

[0053] When a strain gauge 101 is provided on each arm of the Wheatstone bridge, when the distance between the NTC temperature sensor 1021 and the strain gauge 101 on the same arm is relatively close, and the distance between the NTC temperature sensor 1021 and the strain gauges 101 on other arms is relatively far, this difference in distance enables the NTC temperature sensor 1021 to better focus on the temperature compensation of the strain gauge 101 on this arm, improving the pertinence and effectiveness of the compensation, and avoiding the situation of compensation lag where the resistance value of the strain gauge 101 changes due to temperature change, but the resistance value of the NTC temperature sensor 1021 has not started to change yet.

[0054] In practical applications, in order to enable each NTC temperature sensor 1021 to achieve the expected temperature compensation effect on the corresponding strain gauge 101, in some embodiments, the distance between each NTC temperature sensor 1021 and the corresponding strain gauge 101 should be less than or equal to 5 millimeters.

[0055] When there are multiple strain gauges 101 on each arm, when the distance between the NTC temperature sensor 1021 and the strain gauge 101 corresponding to the NTC temperature sensor 1021 is relatively close, it can more quickly and accurately sense the temperature change of the local environment where the strain gauge 101 corresponding to the NTC temperature sensor 1021 is located, so as to perform resistance compensation more timely.

[0056] Based on this, in some embodiments, when at least two strain gauges 101 are provided on each arm of the Wheatstone bridge, for each strain gauge 101, the third distance is less than the fourth distance, and the third distance is less than the fifth distance. The third distance includes the distance between the strain gauge 101 and the corresponding first NTC temperature sensor 1021; the fourth distance includes the distance between the first NTC temperature sensor 1021 and other strain gauges 101 other than the strain gauge 101 corresponding to the first NTC temperature sensor 1021 on the same arm; the fifth distance includes the distance between the first NTC temperature sensor 1021 and the strain gauges 101 on other arms other than the arm where the first NTC temperature sensor 1021 is located.

[0057] Here, through the above distance setting, it can be ensured that each NTC temperature sensor 1021 preferentially compensates the temperature of the nearest strain gauge 101. In this way, more refined and targeted temperature compensation can be achieved. On the premise that the NTC temperature sensor 1021 can better focus on the temperature compensation of the strain gauges 101 on its own arm, the mutual influence of multiple strain gauges 101 on the same arm is fully considered, and the measurement accuracy and reliability of the pressure sensor in complex situations are improved.

[0058] In practical applications, it is necessary to find a resistance compensation device 102 that adapts to the temperature drift characteristics of the strain gauge 101. However, the types of NTC temperature sensors 1021 on the market are limited, and the parameters corresponding to the types of NTC temperature sensors 1021 may not be fully adapted to the temperature drift characteristics of the strain gauge 101.

[0059] Based on this, in some embodiments, as Figure 3 shown, the resistance compensation device 102 may further include a temperature compensation resistor 1022, which is connected in parallel with the NTC temperature sensor 1021. The temperature compensation resistor 1022 and the NTC temperature sensor 1021 are used to compensate in real time the resistance value of the strain gauge 101 generated with the change of the ambient temperature where the strain gauge 101 is located, so that the resistance value of the arm where the strain gauge 101 is located remains constant.

[0060] Here, in actual application, the temperature compensation resistor 1022 is connected in parallel with the NTC temperature sensor 1021, so that the temperature compensation resistor 1022 and the NTC temperature sensor 1021 together exhibit a linear resistance-temperature characteristic, thereby making the resistance compensation device 102 more adaptable to the linear resistance-temperature characteristic of the strain gauge 101. Through the synergistic effect of the NTC temperature sensor 1021 and the temperature compensation resistor 102, the resistance value of the strain gauge 101 can be compensated in real time and more accurately. Specifically, in a parallel circuit, the total resistance is always less than or equal to the smallest resistance among the parallel resistors, that is, the larger resistor contributes less to the total resistance, while the smaller resistor contributes more to the total resistance; the resistance value of the NTC temperature sensor decreases exponentially with increasing temperature. This non-linear resistance-temperature characteristic of the NTC temperature sensor will cause measurement or compensation errors in a wide temperature range; at this time, a temperature compensation resistor with a relatively large fixed resistance value is connected in parallel with the NTC temperature sensor. When the temperature is relatively high, the NTC temperature sensor with a smaller resistance value plays a dominant role in the circuit. As the temperature decreases, the resistance value of the NTC temperature sensor increases, and the total resistance of the parallel circuit is gradually pulled down by the temperature compensation resistor, thereby slowing down the steepness of the change in the resistance value of the NTC temperature sensor, making the curve of the total resistance value changing with temperature tend to be flat, so that the change in the resistance value of the resistance compensation device is closer to linearity and more adaptable to the linear resistance-temperature characteristic of the strain gauge.

[0061] The specific resistance value of the temperature compensation resistor 1022 can be reasonably set according to the characteristics of the resistance changes of the strain gauge 101 and the NTC temperature sensor 1021 with temperature. As a supplement to the NTC temperature sensor 1021, the compensation effect is further optimized, so that the resistance value of the bridge arm where the strain gauge 101 is located can be more stably maintained at the set value, improving the measurement accuracy and stability of the pressure sensor.

[0062] In actual application, the chip resistor has the advantages of small size, high precision, good reliability, convenient installation, low resistance temperature coefficient, etc. Therefore, the chip resistor can be selected as the temperature compensation resistor 1022. That is to say, in some embodiments, the temperature compensation resistor 1022 may include a chip resistor.

[0063] Here, the chip resistor usually uses a low-temperature drift material as the resistor body, such as metal thin films (such as nickel-chromium alloy, tantalum nitride, etc.). The resistance temperature coefficients of these materials are very low, usually at ±25 ppm / °C or lower. A resistance temperature coefficient of ±25 ppm / °C means that whenever the temperature changes by 1°C, the change in the resistance value is only 25×10 -6 , so the resistance value of the chip resistor is little affected by temperature changes.

[0064] In practical applications, when using a chip resistor in parallel with an NTC temperature sensor 1021, the resistance-temperature characteristic curve of the NTC temperature sensor 1021 can be adjusted to make the NTC temperature sensor 1021 as closely match the temperature drift characteristic of the strain gauge 101 as possible.

[0065] Therefore, the position where the chip resistor is set does not need to be closer to the corresponding strain gauge 101 to specifically compensate for the resistance value of the strain gauge 101 that changes with the ambient temperature. The embodiments of the present application do not limit the specific position where the chip resistor is set in the hardware circuit.

[0066] In some embodiments, the resistance value of the chip resistor is related to the resistance value of the corresponding strain gauge 101 in the environment where the chip resistor is located and the resistance value of the corresponding NTC temperature sensor 1021 in the environment where the chip resistor is located.

[0067] Here, by way of example, since the chip resistor is in parallel with the NTC temperature sensor 1021, assuming that a strain gauge 101 is provided on each arm of the Wheatstone bridge, and the set value of the resistance value to be maintained on the arm where it is located is R 臂 , at a certain temperature value, the resistance value of the strain gauge 101 changes and is updated to R 应 , the resistance value of the chip resistor is R 补 , and at this time, the resistance value of the NTC temperature sensor 1021 is R NTC , the resistance value of R 补 is obtained using the following formula:

[0068]

[0069] In practical applications, since the change in the ambient temperature of the pressure sensor will also cause the expansion or contraction of the elastic body, further affecting the measurement accuracy of the sensor. At this time, R 应 can be the resistance value of the strain gauge 101 provided on the elastic body.

[0070] In practical applications, in a variable temperature environment, the chip resistor needs to compensate for the resistance values generated by the strain gauge 101 at all temperatures within the working temperature range.

[0071] Based on this, in some embodiments, the optimal R 补 can be obtained by using the least squares method according to the resistance-temperature characteristic of the strain gauge 101 and the resistance-temperature characteristic of the NTC temperature sensor 1021. The optimal R 补 is obtained using the following formula:

[0072]

[0073] Where E is the objective function of the least squares method, and T iHere, \(T_i\) represents each temperature point, and \(n\) represents the total number of temperature points. The basic idea of this formula is: based on the resistances of the strain gauge 101 and the NTC temperature sensor 1021 at each temperature point, a target function \(E\) is constructed, and a value of \(R\) that minimizes \(E\) can be found through linear regression method. 补 This value of \(R\) is the optimal \(R\). 补 .

[0074] Here, in addition to the least squares method, genetic algorithms, neural networks and other methods can also be used to calculate the optimal \(R\). 补 When using the least squares method, the linear regression method can also be replaced by methods such as the gradient descent method and the Newton method. The embodiments of the present application do not limit the method for obtaining the resistance value of the patch resistor suitable for compensating the strain gauge 101.

[0075] It can be understood that since the change in the ambient temperature where the pressure sensor is located will also cause the expansion or contraction of the elastic body, at this time, the resistance temperature characteristic \(R(T)\) of the strain gauge 101 应 (T i ) can be the resistance temperature characteristic of the strain gauge 101 provided on the elastic body.

[0076] Silicon strain gauges have the advantages of high sensitivity, high precision, small size, good reliability, etc.

[0077] Based on this, in some embodiments, the strain gauge 101 includes a silicon strain gauge.

[0078] Here, in a pressure sensor, strain gauges with high sensitivity and high precision can more accurately sense minute pressure changes, thereby improving the measurement accuracy of the sensor; small size can also better adapt to the miniaturization development trend of the pressure sensor.

[0079] In actual application, the strain gauge 101 on the bridge arm and the resistance compensation device 102 are arranged on the same PCB. Each bridge arm can be designed and manufactured as a relatively independent module, which is convenient for accurately arranging and debugging the component parameters on each bridge arm. At the same time, it is also beneficial for later maintenance and replacement. Arranging the PCBs where each bridge arm is located on a total PCB can achieve the integration of the entire pressure sensor circuit, reduce the complexity of line connection and the failure points, and improve the stability and reliability of the circuit.

[0080] Based on this, in some embodiments, for each bridge arm of the Wheatstone bridge, the strain gauge 101 and the resistance compensation device 102 on the bridge arm are arranged on a first PCB; all the first PCBs are arranged on a second PCB.

[0081] The installation space in the pressure sensor is relatively limited and there are certain shape requirements. The flexible printed circuit board can better adapt to this complex installation environment, facilitating installation operations such as bending and folding. At the same time, it can also make the strain gauge more easily receive external forces and deform, improving the sensitivity and design flexibility of the pressure sensor.

[0082] Based on this, in some embodiments, the first PCB includes an FPC.

[0083] The FPC uses a flexible insulating material (such as polyimide or polyester film) as the substrate, and has extremely high flexibility and thin and light characteristics. The specific material of the FPC in the embodiments of the present application is not limited.

[0084] The pressure sensor provided by the embodiments of the present application includes: a pressure detection circuit and a resistance compensation device 102; wherein, the pressure detection circuit includes a Wheatstone bridge, and one or more strain gauges 101 are arranged on each arm of the Wheatstone bridge; the pressure detection circuit is used to detect force and / or torque in one or more directions; each strain gauge 101 included in the pressure detection circuit is provided with a corresponding resistance compensation device 102, and the resistance compensation device 102 is used to compensate in real time the resistance value of the strain gauge 101 generated as the temperature of the environment where the strain gauge 101 is located changes, so that the resistance value of the arm where the strain gauge 101 is located remains constant. In the pressure sensor provided by the embodiments of the present application, each strain gauge in the Wheatstone bridge is provided with a corresponding resistance compensation device, forming a sub-unit composed of the strain gauge and the resistance compensation device. In each sub-unit, the temperature drift direction of the resistance compensation device is opposite to the temperature drift direction of the strain gauge. In this way, when the pressure sensor is in a variable temperature environment or each strain gauge is at a different temperature, in each sub-unit, the change amount of the resistance values of the strain gauge and the resistance compensation device is offset in real time, making each sub-unit equivalent to an ideal element not affected by temperature in the bridge, so that the resistance value of the arm where the sub-unit is located remains unchanged. Therefore, when the pressure sensor is in a variable temperature environment or multiple strain gauges are at different temperatures, it can still ensure a stable zero output voltage of the bridge. Therefore, the pressure sensor provided by the embodiments of the present application can accurately sense and compensate in real time the resistance value of each strain gauge generated as the temperature of the environment where the strain gauge is located changes, eliminate the temperature drift influence of the strain gauge on each arm of the bridge, enable the pressure sensor to be placed arbitrarily in a place with a temperature gradient, and improve the measurement accuracy and stability of the sensor.

[0085] The strain gauge 101 and the resistance compensation device 102 in the embodiments of the present application can be arranged in a six-axis force sensor. Therefore, based on the above embodiments, the application example of the present application provides a circuit structure schematic diagram of a six-axis force sensor, as Figure 4As shown in the figure; among them, six Wheatstone bridges form a bridge circuit for detecting forces and / or torques in six directions; among them, each of the said Wheatstone bridges is used to measure the force or torque in one direction. Here, the zero output voltages of the six said Wheatstone bridges are UFx, UFy, UFz, UMx, Umy, and UMz respectively, and the input voltage of the six said Wheatstone bridges is Uk;

[0086] During actual application, when a force Fx is applied in the positive horizontal direction to the sensor: the beams on the sides of strain gauges R11 and R13 are compressed, the resistance values of strain gauges R11 and R13 decrease, the beams on the sides of strain gauges R12 and R14 are stretched, the resistance values of strain gauges R12 and R14 increase, and at this time the Wheatstone bridge outputs a voltage UFx; conversely, when a force is applied in the negative horizontal direction to the sensor, the output voltage is -UFx.

[0087] When a force Fy is applied in the positive vertical direction: the beams on the sides of strain gauges R21 and R23 are compressed, the resistance values of strain gauges R21 and R23 decrease, the beams on the sides of strain gauges R22 and R24 are stretched, the resistance values of the strain gauges increase, and at this time the Wheatstone bridge outputs a voltage UFy; conversely, when a force is applied in the negative direction, the output voltage is -UFy.

[0088] When a force Fz is applied in the positive axial direction: the beams on the sides of strain gauges R31, R33, R35, and R37 are greatly stretched, the resistance values of strain gauges R31, R33, R35, and R37 increase by ΔRm, the beams on the sides of strain gauges R32, R34, R36, and R38 are slightly stretched, the resistance values of strain gauges R32, R34, R36, and R38 decrease by ΔRs. Because ΔRm > ΔRs, at this time the Wheatstone bridge outputs a voltage UFz; conversely, when a force is applied in the negative direction, the output voltage is -UFz.

[0089] When a pitching moment Mx is applied in the positive direction: the beams on the sides of strain gauges R41 and R43 are compressed, the resistance values of strain gauges R41 and R43 decrease, the beams on the sides of strain gauges R42 and R44 are stretched, the resistance values of strain gauges R42 and R44 increase, and at this time the Wheatstone bridge outputs a voltage UMx; conversely, when a force is applied in the negative direction, the output voltage is -UMx.

[0090] When a rolling moment My is applied in the positive direction: the beams on the sides of strain gauges R51 and R53 are compressed, the resistance values of strain gauges R51 and R53 decrease, the beams on the sides of strain gauges R52 and R54 are stretched, the resistance values of strain gauges R52 and R54 increase, and at this time the Wheatstone bridge outputs a voltage UMy; conversely, when a force is applied in the negative direction, the output voltage is -Umy.

[0091] When applying a positive yaw moment Mz: The beams on the sides of strain gauges R61, R63, R65, and R67 are compressed, the resistance values of strain gauges R61, R63, R65, and R67 decrease, the beams on the sides of strain gauges R62, R64, R66, and R68 are stretched, the resistance values of strain gauges R62, R64, R66, and R68 increase, and at this time, the Wheatstone bridge outputs a voltage UMz; conversely, when applying a negative force, the output voltage is -UMz.

[0092] In Figure 4 , only the NTC temperature sensors and chip resistors of the bridge for detecting the horizontal force Fx are marked, and the NTC temperature sensors and chip resistors of the bridges for detecting forces in other directions are not marked; taking the bridge for detecting the horizontal force Fx as an example, the zero-point output voltage is calculated below.

[0093] When the bridge for detecting the horizontal force is subjected to the force Fx, assume that the total resistance of the bridge arm where strain gauge R11 is located is R1; the total resistance of the bridge arm where strain gauge R12 is located is R2; the total resistance of the bridge arm where strain gauge R13 is located is R3; the total resistance of the bridge arm where strain gauge R14 is located is R4; according to Ohm's law and Kirchhoff's law, the zero-point output voltage UFx is obtained using the following formula:

[0094] UFx = I1R1 - I2R4 (3)

[0095] Among them, I1 is the current flowing through strain gauges R11 and R12; I2 is the current flowing through strain gauges R13 and R14. The following formula is used to obtain the total resistance of each bridge arm and the values of I1 and I2:

[0096]

[0097] Among them, Ra, R NTC1 are the temperature compensation resistors and NTC temperature sensors for compensating strain gauge R11 respectively; Rb, R NTC2 are the temperature compensation resistors and NTC temperature sensors for compensating strain gauge R12 respectively; Rc, R NTC3 are the temperature compensation resistors and NTC temperature sensors for compensating strain gauge R13 respectively; Rd, R NTC4 are the temperature compensation resistors and NTC temperature sensors for compensating strain gauge R14 respectively. Based on formulas (3)-(5), the zero-point output voltage UFx is obtained using the following formula:

[0098]

[0099] Assume that the initial resistances of each bridge arm are R1 = R2 = R3 = R4, the bridge satisfies the balance condition, the bridge is initially in a balanced state, and UFx = 0; when the sensor is in the process of heating up or cooling down, or when each bridge arm is placed in different temperature scenarios, or when the sensor is constantly subjected to thermal shock, due to the compensation of the NTC temperature sensors and temperature compensation resistors corresponding to each strain gauge, R1 = R2 = R3 = R4 can still be maintained, making UFx = 0.

[0100] When the bridge for detecting the horizontal force Fx is subjected to the force Fx and the sensor is not affected by temperature drift, the resistances of R11, R12, R13, and R14 change, and R NTC1 , R NTC2 , R NTC3 , R NTC4 and the resistance values of Ra, Rb, Rc, and Rd do not change; at this time, the resistance values of R1, R2, R3, and R4 change, corresponding to R1', R2', R3', and R4' respectively. The changed R1', R2', R3', and R4' are obtained using the following formula:

[0101]

[0102] where ΔR1, ΔR2, ΔR3, and ΔR4 are the resistance change amounts of R1, R2, R3, and R4 respectively; at this time, the zero-point output voltage UFx is obtained using the following formula:

[0103]

[0104] It can be understood that the method for obtaining the zero-point output voltage of the bridge for detecting forces or torques in other directions can all refer to the method for obtaining the zero-point output voltage of the bridge for detecting the horizontal force Fx, which will not be elaborated here.

[0105] Based on the above embodiments, the application example of the present application provides a structural schematic diagram of a six-axis force sensor, as Figure 5 shown, Figure 5 showing Figure 4 the specific positions of each strain gauge on each bridge arm of each Wheatstone bridge on the six-axis force sensor, for presenting Figure 4 the actual assembly and layout of each component in the circuit; in Figure 5 , only the NTC temperature sensor and the chip resistor of the bridge for detecting the horizontal force Fx are marked, and the NTC temperature sensors and chip resistors of the bridges for detecting forces in other directions are not marked.

[0106] Taking the bridge for detecting the horizontal force Fx as an example, the positions of the NTC temperature sensor and the chip resistor will be described below.

[0107] FromFigure 5 As can be seen, for each arm of each Wheatstone bridge, the strain gauge (i.e., the above-mentioned strain gauge 101) and the resistance compensation device (i.e., the above-mentioned resistance compensation device 102) on the arm are arranged on the same transition PCB (i.e., the above-mentioned first PCB); the NTC temperature sensors (i.e., the above-mentioned NTC temperature sensors 1021) corresponding to the respective strain gauges are closest to the strain gauges to be compensated. Taking the bridge for detecting the horizontal force Fx as an example, as Figure 5 shown, the NTC temperature sensor R NTC1 is closest to the strain gauge R11, the NTC temperature sensor R NTC2 is closest to the strain gauge R12, the NTC temperature sensor R NTC3 is closest to the strain gauge R13, and the NTC temperature sensor R NTC4 is closest to the strain gauge R14. This difference in distance enables the NTC temperature sensor to better focus on the temperature compensation of the strain gauge on this arm, improving the pertinence and effectiveness of the compensation. And the patch resistors only need to be on the same transition PCB as the strain gauges they correspond to, that is, the patch resistors Ra, Rb, Rc, and Rd do not need to be closer to the strain gauges R11, R12, R13, and R14 they correspond to respectively, and can compensate the resistance value of the strain gauge caused by the change in the ambient temperature where it is located.

[0108] It can be understood that the arrangement method of the NTC temperature sensors and the patch resistors corresponding to the strain gauges on the bridges for detecting forces or torques in other directions is the same as that of the NTC temperature sensors and the patch resistors corresponding to the strain gauges on the bridge for detecting the horizontal force Fx, which will not be elaborated here.

[0109] It should be noted that in this article, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such a process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including that element.

[0110] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of the said features. In the description of the embodiments of the present application, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined. It should be noted that "first", "second", etc. are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence.

[0111] It should be understood that "some embodiments" mentioned throughout the specification mean that specific features, structures, or characteristics related to the embodiments are included in at least one embodiment of the present application. Therefore, "in some embodiments" appearing throughout the specification does not necessarily refer to the same embodiments. In addition, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments without conflict.

[0112] The term "and / or" in this document is merely a description of the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone.

[0113] In the description of the embodiments of the present application, it should be noted that unless otherwise clearly specified and limited, terms such as "connected" or "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a connection that allows mutual communication; it can be directly connected, or indirectly connected through an intermediate medium, and can be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0114] In addition, the technical solutions described in the embodiments of the present application can be arbitrarily combined without conflict.

[0115] The above is only a preferred embodiment of the present application and is not intended to limit the protection scope of the present application.

Claims

1. A pressure sensor, characterized in that: include: Pressure detection circuit and resistance compensation device; wherein, The pressure detection circuit comprises a Wheatstone bridge, and each bridge arm of the Wheatstone bridge is provided with one or more strain gauges; the pressure detection circuit is used to detect force and / or torque in one or more directions; Each strain gauge included in the pressure detection circuit is provided with a corresponding resistance compensation device, and the resistance compensation device is used to compensate in real time the resistance value of the strain gauge generated by the change of the ambient temperature of the strain gauge, so as to keep the resistance value of the bridge arm where the strain gauge is located constant.

2. The pressure sensor according to claim 1, characterized in that: The resistance compensation device comprises a negative temperature coefficient (NTC) temperature sensor, which is arranged on the bridge arm where the corresponding strain gauge is located and is connected in series with the corresponding strain gauge.

3. The pressure sensor according to claim 2, characterized in that: When a strain gauge is arranged on each bridge arm of the Wheatstone bridge, the first distance is smaller than the second distance, and the first distance includes the distance between the NTC temperature sensor and the strain gauge on the same bridge arm where the NTC temperature sensor is located; and the second distance includes the distance between the NTC temperature sensor and the strain gauge on other bridge arms other than the bridge arm where the NTC temperature sensor is located.

4. The pressure sensor according to claim 2, when at least two strain gauges are arranged on each bridge arm of the Wheatstone bridge, for each strain gauge, the third distance is less than the fourth distance, the third distance is less than the fifth distance, the third distance includes the distance between the strain gauge and the corresponding first NTC temperature sensor; the fourth distance includes the distance between the first NTC temperature sensor and other strain gauges other than the strain gauge corresponding to the first NTC temperature sensor on the same bridge arm, and the fifth distance includes the distance between the first NTC temperature sensor and strain gauges on other bridge arms other than the bridge arm where the first NTC temperature sensor is located.

5. The pressure sensor according to claim 2, characterized in that: The resistance compensation device also includes a temperature compensation resistor, which is connected in parallel with the NTC temperature sensor. The temperature compensation resistor and the NTC temperature sensor are used to compensate in real time for the resistance value of the strain gauge generated by changes in the ambient temperature of the strain gauge, so that the resistance value of the bridge arm where the strain gauge is located remains constant.

6. The pressure sensor according to claim 5, characterized in that: The temperature compensation resistor includes a chip resistor.

7. The pressure sensor according to claim 6, characterized in that: The resistance value of the patch resistor is associated with the resistance value of the strain gauge corresponding to the patch resistor in the environment in which it is located and the resistance value of the NTC temperature sensor corresponding to the patch resistor in the environment in which it is located.

8. The pressure sensor according to claim 1, characterized in that: The strain gauge comprises a silicon strain gauge.

9. The pressure sensor according to any one of claims 1 to 8, characterized in that: For each bridge arm of the Wheatstone bridge, the strain gauge and the resistance compensation device on the bridge arm are arranged on a first printed circuit board PCB; and all the first PCBs are arranged on a second PCB.

10. The pressure sensor according to claim 9, characterized in that: The first PCB includes a flexible circuit board FPC.

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