Device and method for improving torque calibration precision

Abstract

A first supporting seat and a second supporting seat are both arranged on a base, the top of the first supporting seat is provided with a bearing seat used for supporting an elastic shaft, the top of the second supporting seat is provided with a torque sensor to be calibrated, and the torque sensor is connected with a lever through the elastic shaft; applying torque to the elastic shaft through lever imbalance; during calibration, the movable weight is suspended at one end of the lever, the fixed weight is suspended at the other end of the lever, and the additional weight is suspended at the bottom of the fixed weight. The laser interferometer is arranged on the outer side of one end of the lever and used for measuring displacement of the movable weight, and the reflector is arranged on the lever and synchronously moves along with the movable weight. The method can be applied to calibration work of high-precision torque measuring instruments in the fields of industry, spaceflight and the like.

Description

Technical Field

[0001] The present invention relates to torque calibration technology, and more specifically, to a device and method for improving torque calibration accuracy. Background Art

[0002] With the continuous progress of science and technology, torque measurement technology has been widely applied in many fields such as industry, aerospace, agriculture, and military. Therefore, higher requirements are put forward for torque measurement accuracy. Calibrating the torque sensor can ensure the accuracy of its measured value, ensure the normal operation of the equipment, and increase the service life of the equipment.

[0003] The commonly used calibration principle adopts the lever-weight type static calibration method. Based on the lever principle, a known acting force F is applied to a standard lever with a length of L, thereby constructing a standard torque reference quantity. The value traceability system of this method has a clear physical basis: the torque value can be traced back to the basic physical quantities - the mass reference m and the length reference L. Although modern precision machining technology can achieve a micron-level measurement accuracy of the lever arm length, due to problems such as the deviation of the center of mass of the weight, the offset of the lever fulcrum, and the deformation drift of the center of the rotating shaft in actual working conditions, the coupling effect of these error sources will introduce systematic deviations, resulting in a reduction in the calibration accuracy of the sensor. The currently commonly used calibration method assumes that the center of the elastic shaft and the position of the lever fulcrum are fixed, and the center of gravity of the weight is idealized as a mass point, making it difficult to directly measure or correct the coupling error caused by the above error sources, resulting in the accumulation of systematic errors, thereby reducing the torque measurement accuracy. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art, and a device and method for improving torque calibration accuracy are proposed, which have the advantages of high precision and strong adaptability. Based on the lever structure, the position and mass of the weight are adjusted simultaneously to realize the self-calibration of the force arm length, so as to eliminate the influence of the offset between the axis of the elastic shaft and the lever fulcrum and the deviation of the center of gravity of the weight on torque measurement.

[0005] The purpose of the present invention can be achieved by the following technical solutions.

[0006] A device for improving torque calibration accuracy includes a base frame, a weight loading mechanism, and a displacement measurement mechanism;

[0007] The base frame includes a base, a first support seat, a lever, and a second support seat. The first support seat and the second support seat are both arranged on the base. A bearing seat for supporting the elastic shaft is arranged at the top of the first support seat. A torque sensor to be calibrated is installed at the top of the second support seat. The torque sensor is connected to the lever through the elastic shaft, and torque is applied to the elastic shaft by the imbalance of the lever;

[0008] The weight loading mechanism includes a movable weight, a fixed weight, and an additional weight. During calibration, the movable weight is suspended at one end of the lever and can move horizontally along the lever. The fixed weight is suspended at the other end of the lever, and the additional weight is suspended at the bottom of the fixed weight.

[0009] The displacement measuring mechanism includes a laser interferometer and a reflector. The laser interferometer is arranged outside one end of the lever and close to the movable weight side for measuring the displacement of the movable weight. The reflector is arranged on the lever and moves synchronously with the movable weight.

[0010] Furthermore, preferably, a locking seat is also arranged on the base. The second support seat is located between the locking seat and the first support seat. One side of the torque sensor is fixedly connected to the locking seat, and the other side is connected to one end of the rotating shaft through a coupling. The other end of the rotating shaft passes through the bearing seat and is fixedly connected to the weight tray. The weight tray is fixedly connected to the fulcrum position of the lever.

[0011] Furthermore, preferably, a guide rail is arranged along the length direction of the lever and is driven by a stepping motor to drive the movable weight to realize displacement adjustment along the lever direction. The reflector is arranged on the guide rail and moves synchronously with the movable weight.

[0012] The object of the present invention can also be achieved by the following technical solutions.

[0013] A method for improving the torque calibration accuracy includes the following steps:

[0014] S1: Initial balance state

[0015] Suspend the movable weight and the fixed weight with the same mass of m symmetrically on both sides of the lever. At this time, the force arms L1 of the movable weight and L2 of the fixed weight are equal, both set as L0. Detect and ensure that the lever is in a balanced state when it is stationary. Align the laser interferometer with the reflector and record the initial position.

[0016] S2: Introduce an additional weight

[0017] Suspend an additional weight with a mass of Δm directly below the fixed weight. A torque increment is generated on one side of the lever, and the lever generates an inclination angle due to torque imbalance.

[0018] S3: Measure the displacement increment

[0019] Move the movable weight until the lever reaches a balanced state again, and at the same time use the laser interferometer to measure the displacement increment ΔL of the movable weight.

[0020] S4: Force arm calibration

[0021] Calculate the actual force arm L0 of the fixed weight before the introduction of the additional weight according to the following formula:

[0022] L0 = m·ΔL / Δm

[0023] S5: Torque calibration

[0024] Remove the movable weights and additional weights, and only hang the fixed weights at the actual arm L0. Within the range of the torque sensor to be calibrated, use the multi-point calibration method to gradually increase the mass of the fixed weights for calibration. Calculate the theoretical torque values of each calibration point according to the following torque formula, and compare them with the output torque values of the torque sensor to be calibrated to complete the calibration of the torque sensor;

[0025] T i = m i gL0

[0026] In the formula, T i is the theoretical torque value of the i-th calibration point, and m i is the mass of the fixed weights at the i-th calibration point.

[0027] Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are:

[0028] The present invention designs a device and method for improving the accuracy of torque calibration. By simultaneously adjusting the displacement increment ΔL of the movable weights and the mass increment Δm of the additional weights, errors such as the deviation of the centroid of the weights, the offset of the lever fulcrum, and the deformation drift of the shaft center in traditional calibration can be eliminated, and the influence of the system error source on the torque calibration result is reduced. This method significantly improves the accuracy of the calibration result and provides an efficient and low-cost solution for the calibration of high-precision torque values. Description of the Drawings

[0029] Figure 1 is a schematic diagram of the initial balance state of the device for improving the torque calibration accuracy of the present invention;

[0030] Figure 2 is a schematic diagram of the principle of the initial balance state of the device for improving the torque calibration accuracy of the present invention;

[0031] Figure 3 is a schematic diagram of the secondary balance state of the device for improving the torque calibration accuracy of the present invention;

[0032] Figure 4 is a schematic diagram of the principle of the secondary balance state of the device for improving the torque calibration accuracy of the present invention.

[0033] Reference numerals: 1 - base, 2 - first support seat, 3 - lever, 4 - torque sensor, 5 - laser interferometer, 6 - mirror, 7 - movable weight, 8 - fixed weight, 9 - locking seat, 10 - additional weight, 11 - weight tray, 12 - second support seat, 13 - bearing seat. Detailed Embodiments

[0034] To make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] In order to improve the accuracy of torque calibration, based on the lever principle, the present invention designs a method for improving the accuracy of torque calibration.

[0036] Embodiment 1

[0037] The present invention provides a device for improving the accuracy of torque calibration, which mainly includes a base bench, a weight loading mechanism, and a displacement measurement mechanism. Each part cooperates to complete the calibration work. By simultaneously adjusting the mass increment of the weights and the displacement increment, the force arm is self-calibrated, thereby eliminating the systematic errors introduced by error sources such as the centroid deviation of the weights, the offset of the lever fulcrum, and the deformation drift of the rotating shaft center in traditional torque measurement.

[0038] (1) Base bench

[0039] As Figure 1 shown, the base bench mainly includes a base 1, a first support seat 2, a lever 3, and a second support seat 12. The first support seat 2 and the second support seat 12 are both arranged on the base 1. A bearing seat 13 for supporting the elastic shaft is provided at the top of the first support seat 2. A torque sensor 4 to be calibrated is installed at the top of the second support seat 12. The torque sensor 4 is connected to the lever 3 through an elastic shaft. When the lever 3 rotates out of balance, a torque is applied to the elastic shaft. The lengths of the force arms on both the left and right sides of the lever 3 are adjustable to establish a balanced state.

[0040] In the above base bench, preferably, a locking seat 9 is further provided on the base 1. The second support seat 12 is located between the locking seat 9 and the first support seat 2. One side of the torque sensor 4 is fixedly connected to the locking seat 9, and the other side is connected to one end of a rotating shaft through a coupling. The other end of the rotating shaft passes through the bearing seat and is fixedly connected to a weight disc 11. The weight disc 11 is fixedly connected to the fulcrum position of the lever 3.

[0041] Among them, the base 1, the support seat 2, the lever 3, and the locking seat 9 can all be made of high-rigidity materials, such as aluminum alloy, etc. A highly sensitive bearing that can rotate relative to it is installed in the bearing seat 13, such as a silicon nitride ceramic bearing, etc., which can ensure the sensitivity and stability when the torque is balanced. A keyway connection method can be adopted between the weight disc 11 and the elastic shaft, and the weight disc 11 and the lever 3 can be fixedly connected by bolts.

[0042] (2) Weight loading mechanism

[0043] The weight loading mechanism includes a movable weight 7, a fixed weight 8, and an additional weight 10. During calibration, the movable weight 7 is suspended at one end of the lever 3 (the left side in the figure), and can move horizontally along the lever 3. The fixed weight 8 is suspended at the other end of the lever 3 (the right side in the figure) and cannot move. The additional weight 10 is suspended at the bottom of the fixed weight 8.

[0044] In the above-mentioned weight loading mechanism, preferably, a guide rail is provided along the length direction of the lever 3, which is driven by a stepper motor to drive the movable weight 7 to achieve displacement adjustment with micron-level accuracy along the direction of the lever 3. The guide rail can adopt a ball screw.

[0045] In the above-mentioned weight loading mechanism, preferably, the movable weight 7, the fixed weight 8, and the additional weight 10 can be made of 316L stainless steel. The movable weight 7 and the fixed weight 8 have the same mass. The additional weight 10 is a standard weight with a known mass. The additional weight 10 is suspended below the fixed weight 8 through a hook to increase the moment on the corresponding side and introduce a controllable torque disturbance. By applying the additional weight 10 with a known mass increment to introduce torque disturbance, and controlling the precise movement of the movable weight 7 along the direction of the force arm, the lever can be rebalanced.

[0046] (3) Displacement measurement mechanism

[0047] The displacement measurement mechanism includes a laser interferometer 5 and a reflector 6. The laser interferometer 5 is arranged outside one end of the lever 3 and close to the movable weight 7 for measuring the displacement increment of the movable weight 7. The reflector 6 is installed on the guide rail of the lever 3 and moves synchronously with the movable weight 7.

[0048] The laser interferometer 5 maintains a certain measurement distance from the movable weight 7. When the movable weight 7 undergoes displacement, it simultaneously drives the reflector 6 to change its position. The laser interferometer 5 is used to emit laser light and capture the change in the reflection angle of the reflector 6 in real time. Through the built-in algorithm, the displacement increment ΔL of the movable weight 7 can be accurately calculated to achieve high-precision non-contact measurement.

[0049] Embodiment 2

[0050] Based on the device principle of the above Embodiment 1, this embodiment also proposes a method for improving the torque calibration accuracy, including the following steps:

[0051] S1: Initial equilibrium state

[0052] In the initial state, as Figure 2As shown in the figure, the movable weights 7 and the fixed weight 8, each with a mass of m, are symmetrically suspended on both sides of the lever 3. The movable weight 7 can move along the direction of the lever arm, with the lever arm being L1, and the position of the fixed weight 8 is fixed, with the lever arm being L2. Using an electronic level (resolution 0.001°) for detection, ensure that the lever 3 is in a balanced state (tilt angle ≤ ±0.002°) when it is stationary, and the lever arms L1 of the movable weight 7 and L2 of the fixed weight 8 are equal. Align the laser interferometer 5 with the mirror 6 and record the initial position.

[0053] In addition, in the initial state, the installation accuracy can also be verified by a laser interferometer (linear accuracy ±0.5 μm / m). The measurement reference distance of the laser interferometer 5 is 500 mm, the displacement resolution reaches 0.1 nm, and the parallelism error between the optical axis and the moving trajectory of the weight A is ≤ 0.001°.

[0054] The lever arms L1 of the movable weight 7 and L2 of the fixed weight 8 are equal, both set as L0, and satisfy the following relationship:

[0055] L1 = L2 = L0 (1)

[0056] At this time, the reverse torque value T on the side of the movable weight 7 0- is:

[0057] T 0- = mgL1 = mgL0 (2)

[0058] At this time, the reverse torque value T on the side of the fixed weight 8 0+ is:

[0059] T 0+ = mgL2 = mgL0 (3)

[0060] S2: Introduce an additional weight

[0061] Suspend an additional weight 9 with a mass of Δm directly below the fixed weight 8. A moment increment is generated on one side of the lever 3, and the lever 3 generates an inclination angle due to torque imbalance.

[0062] For example: The mass of the additional weight 9 is Δm = 0.0500 kg. This weight is made of 316L stainless steel, and the centroid deviation is ≤ ±0.1 mm. The additional weight 9 is suspended directly below the fixed weight 8 through a high-rigidity titanium alloy hook.

[0063] S3: Measure the displacement increment

[0064] Drive the movable weight 7 to move along the lever arm until the lever 3 reaches a balanced state again. At the same time, use the laser interferometer 5 to accurately measure the displacement increment ΔL of the movable weight 7, as shown in Figure 3 and Figure 4 shown. During this process, an electronic level can be used to detect the balanced state of the lever 3.

[0065] At this time, the torque relationship on both sides of the lever arm satisfies:

[0066] mg(L1+ΔL)=(m+Δm)gL2(4)

[0067] S4: Arm calibration

[0068] By combining equations (1) and (4), the system error can be eliminated and the actual force arm L0 of the fixed weight 8 before the additional weight 9 is introduced can be calculated according to the following formula:

[0069] L0=m·ΔL / Δm(5)

[0070] Through the precise measurement of laser interferometer and electronic balance, Δm and ΔL can reach extremely high accuracy level. m is a known quantity. At this time, L0 can be converted into a deterministic physical quantity directly characterized by the parameters mass m, mass increment Δm and displacement increment ΔL.

[0071] S5: Torque calibration

[0072] In order to further improve the calibration reliability, within the range of the torque sensor 4 to be calibrated (e.g. (rated torque 20 N·m), etc.), a multi-point calibration method is adopted, and multiple calibration points (20%, 40%, 60%, 80%, 100%) can be selected in proportion. The movable weight 7 and the additional weight 9 are removed, and only the fixed weight 8 is hung at the actual force arm L0. The mass of the fixed weight 8 is gradually increased for calibration. The theoretical torque value of each calibration point is calculated according to the following torque formula (6), and compared with the output torque value of the torque sensor 4 to be calibrated, and the relative error between the two is calculated for analysis, thereby completing the high-precision calibration of the torque sensor.

[0073] T i =m i gL0(6)

[0074] Where, T i is the theoretical torque value of the ith calibration point, m i is the mass of the fixed weight at the i-th calibration point. In this process, each calibration point can be tested repeatedly to eliminate gross errors.

[0075] In summary, the torque calibration method designed in the present invention uses only relatively simple mechanical elements and has a simple structure. By adjusting the position and mass of the weights at the same time, the system error introduced by the error sources such as the weight center deviation, the lever fulcrum offset, and the shaft center deformation drift in the traditional static calibration is eliminated, and the torque calibration accuracy is significantly improved.

[0076] Although the functions and working processes of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific functions and working processes described above. The above specific embodiments are merely illustrative rather than restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose of the present invention and the scope protected by the claims, and these all fall within the protection scope of the present invention.

Claims

1. A device for improving torque calibration accuracy, characterized in that: It includes a base frame, a weight loading mechanism, and a displacement measuring mechanism; The base frame comprises a base (1), a No. 1 support seat (2), a lever (3), and a No. 2 support seat (12); the No. 1 support seat (2) and the No. 2 support seat (12) are both arranged on the base (1); a bearing seat (13) for supporting an elastic shaft is arranged on the top of the No. 1 support seat (2); a torque sensor (4) to be calibrated is installed on the top of the No. 2 support seat (12); the torque sensor (4) is connected to the lever (3) via the elastic shaft, and torque is applied to the elastic shaft via the imbalance of the lever (3); The weight loading mechanism comprises a movable weight (7), a fixed weight (8), and an additional weight (10). During calibration, the movable weight (7) is suspended at one end of the lever (3) and can move horizontally along the lever (3), the fixed weight (8) is suspended at the other end of the lever (3), and the additional weight (10) is suspended at the bottom of the fixed weight (8); The displacement measuring mechanism comprises a laser interferometer (5) and a reflector (6); the laser interferometer (5) is arranged outside one end of the lever (3) and close to a side of a movable weight (7) for measuring the displacement of the movable weight (7); and the reflector (6) is arranged on the lever (3) and moves synchronously with the movable weight (7).

2. The device for improving torque calibration accuracy according to claim 1, characterized in that: The base (1) is also provided with a locking seat (9), the second support seat (12) is located between the locking seat (9) and the first support seat (2), one side of the torque sensor (4) is fixedly connected to the locking seat (9), and the other side is connected to one end of the rotating shaft through a coupling, the other end of the rotating shaft passes through the bearing seat (13) and is fixedly connected to the weight plate (11), and the weight plate (11) is fixedly connected to the fulcrum position of the lever (3).

3. The device for improving torque calibration accuracy according to claim 1, characterized in that: The lever (3) is provided with a guide rail along its length direction, which is driven by a stepping motor to drive the movable weight (7) to achieve displacement adjustment along the direction of the lever (3); the reflector (6) is arranged on the guide rail and moves synchronously with the movable weight (7).

4. A method for improving torque calibration accuracy using the device for improving torque calibration accuracy according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Initial equilibrium state A movable weight (7) and a fixed weight (8) both of which have a mass of m are symmetrically suspended on both sides of the lever (3). At this time, the force arm L1 of the movable weight (7) and the force arm L2 of the fixed weight (8) are equal, both set to L0. Check to ensure that the lever (3) is in a balanced state when it is stationary. Aim the laser interferometer (5) at the reflector (6) and record the initial position. S2: Introduction of additional weights An additional weight (9) with a mass of Δm is suspended directly below the fixed weight (8), a torque increment is generated on one side of the lever (3), and the lever (3) is tilted due to the torque imbalance; S3: Measuring displacement increments Moving the movable weight (7) until the lever (3) reaches a balanced state again, and measuring the displacement increment ΔL of the movable weight (7) by using a laser interferometer (5); S4: Arm calibration The actual force arm L0 of the fixed weight (8) before the additional weight (9) is introduced is calculated according to the following formula: L0=m·ΔL / Δm S5: Torque calibration Remove the movable weight (7) and the additional weight (9), and only hang the fixed weight (8) at the actual force arm L0. Within the range of the torque sensor (4) to be calibrated, use the multi-point calibration method to gradually increase the mass of the fixed weight (8) for calibration. Calculate the theoretical torque value of each calibration point according to the following torque formula, and compare it with the output torque value of the torque sensor (4) to complete the calibration of the torque sensor; T i =m i gL0 Where, T i is the theoretical torque value of the ith calibration point, m i is the mass of the fixed weight at the i-th calibration point.

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