A method for built-in torque measurement in a harmonic reducer based on independent gain adjustment and a torque sensor system

Abstract

The application belongs to the field of robot sensing technology, and discloses a built-in torque measurement method of a harmonic reducer based on independent gain adjustment, wherein M strain gauges are arranged on the surface of the diaphragm part of the flexspline of the harmonic reducer; the number M of the strain gauges satisfies M≥2N+1, wherein N is the highest order of the frequency component of the corrugation interference signal to be compensated. In order to eliminate the N frequency components of the corrugation, the application needs at least 2N+1 strain gauges. Therefore, by arranging 3 or more strain gauges (for example, M≥3) on the diaphragm part of the flexspline, a sensing array with information redundancy is formed, so that the system has sufficient degrees of freedom to simultaneously represent the real torque signal and the corrugation interference of multiple frequency components.

Description

Technical Field

[0001] This invention belongs to the field of robot sensing technology, specifically relating to a method for measuring the torque of a harmonic reducer based on independent gain adjustment and a torque sensor system. Background Technology

[0002] Among various transmission mechanisms, harmonic reducers are widely used in high-dynamic performance scenarios such as industrial robots, collaborative robots, aerospace robotic arms, and medical surgical robots due to their advantages of compact structure, large transmission ratio, small backlash, and high precision. To meet the requirements of closed-loop force control, traditional solutions typically place an external torque sensor at the output end of the harmonic reducer. However, the current mainstream method for internal torque measurement involves attaching resistance strain gauges to the surface of the flexspline of the harmonic reducer and converting the strain signal into a voltage output through a Wheatstone bridge circuit, thereby inverting the output torque. While this method has advantages such as simple structure and fast response, it is limited by the unique working mechanism of the harmonic reducer—the flexspline is forced to undergo periodic elliptical deformation under the action of the wave generator. This causes the strain gauge to not only respond to the stress caused by the actual torque but also to be superimposed with periodic interference signals caused by the elliptical deformation that are strongly correlated with the rotor position and speed, which is often referred to in the industry as "ripples."

[0003] To suppress this ripple interference, existing technologies often employ symmetrically arranged two or four strain gauges to form a full-bridge or half-bridge circuit, attempting to cancel common-mode interference in the circuit through physical symmetry. However, due to unavoidable micron-level positional deviations, material anisotropy, and non-ideal elliptical deformation of the flexspline during manufacturing and assembly, the actual strain field distribution is difficult to be completely symmetrical, especially since higher-order harmonic components cannot be effectively canceled (the residual error is approximately 4% of the maximum torque).

[0004] Another type of solution attempts to introduce digital signal processing techniques, such as using Kalman filters, low-pass filters, or adaptive filtering algorithms to post-process the original signal to suppress ripple. However, such methods typically introduce a computational delay of about 1 millisecond, significantly reducing the system control bandwidth and affecting dynamic response performance, especially posing safety risks in scenarios such as high-speed trajectory tracking or sudden collision detection. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for measuring torque in a harmonic reducer based on independent gain adjustment and a torque sensor system, so as to solve the problems existing in the background art.

[0006] To solve the above-mentioned technical problems, the first technical solution of the present invention is a method for measuring the built-in torque of a harmonic reducer based on independent gain adjustment, which includes the following steps;

[0007] Step 1: Arrange M strain gauges on the diaphragm surface of the flexure of the harmonic reducer;

[0008] Step 2: Configure an independent signal amplification channel for each strain gauge, with each signal amplification channel having a corresponding adjustable gain coefficient. ;

[0009] Step 3: During the operation of the harmonic reducer, the original output signal of each strain gauge is collected synchronously;

[0010] Step 4: Based on the original output signal, adjust the gain coefficient of the corresponding signal amplification channel. This ensures that the periodic ripple components related to the rotation of the harmonic reducer in the output signal of each strain gauge after gain adjustment cancel each other out after weighted summation, thereby minimizing the output of the total ripple signal.

[0011] Step 5: Sum the output signals of all signal amplification channels after gain adjustment as the final torque measurement value.

[0012] Preferably, the number M of strain gauges satisfies M≥2N+1, where N is the highest order of the frequency component of the ripple interference signal to be compensated.

[0013] Furthermore, the number M of the strain gauges is an odd number.

[0014] Furthermore, the number of strain gauges M is at least 3, used to compensate for the fundamental frequency component of the ripple signal.

[0015] Furthermore, when M=3, three strain gauges are arranged circumferentially on the surface of the flexure diaphragm section, and the positional interval of the strain gauges corresponds to one-third of the fundamental frequency period of the ripple signal; or they are arranged symmetrically on opposite sides of the flexure.

[0016] Furthermore, in step 4, the gain coefficient is determined. The method employs a "deterministic approach," and step 4 includes establishing a model containing the amplitude of the ripple signal. and phase The homogeneous linear equation system:

[0017] ;

[0018] in, m is the gear design coefficient. The input shaft rotation angle is used; the amplitude and phase of each strain gauge signal are obtained through Fourier transform, one of the gain values ​​is preset, the equations are solved to obtain the relative values ​​of the remaining gains, and finally all gains are adjusted by scaling factors to match the required torque sensitivity.

[0019] Preferably, the gain coefficient is determined in step 4. The method employs a "heuristic approach." Step 4 includes weighted summation of the output signals of all strain gauges after gain adjustment to obtain a composite signal; monitoring the peak value of the composite signal during the operation of the harmonic reducer; and fine-tuning the gain of each channel until the ripple amplitude in the composite signal reaches its minimum.

[0020] Preferably, the strain gauge is attached to the inner or outer side of the flexible diaphragm portion.

[0021] Furthermore, the strain gauge is attached to the inner side of the flexible diaphragm near the hub, and the lead wire is fixed to the stationary hub to improve the durability of the sensor under long-term operation.

[0022] To address the aforementioned technical problems, the second technical solution of this invention is a harmonic reducer torque sensor system that applies the built-in torque measurement method of the harmonic reducer described in the first technical solution. The system includes a harmonic reducer body; multiple strain gauges attached to the flexural diaphragm portion; a multi-channel analog amplification circuit corresponding to each strain gauge, with each channel having an independently adjustable gain; a summing circuit for weighted summation of the output signals from all amplified signal channels; and the output of the summing circuit provides a ripple-compensated torque measurement signal.

[0023] The main technical effects of this invention are reflected in the following aspects:

[0024] Traditional Wheatstone bridges rely on two or four strictly symmetrically arranged strain gauges, which can only cancel the ideal fundamental frequency component and cannot cope with actual mounting errors, material inhomogeneities, and higher-order harmonics. This invention requires at least 2N+1 strain gauges to eliminate ripples in N frequency components. Therefore, by arranging three or more strain gauges (e.g., M≥3) on the flexible diaphragm section, a redundant sensing array is formed, giving the system sufficient degrees of freedom to simultaneously characterize the real torque signal and ripple interference from multiple frequency components.

[0025] This invention configures an independent signal amplification channel for each strain gauge, and the gain of each channel can be set individually. By adjusting these gain coefficients, the ripple components in the weighted sum of the output signals of each channel cancel each other out, while the torque-related components are retained and enhanced. Since the entire process is completed at the analog front end or high-speed digitization, without relying on iterative filtering or state estimation, no significant computational delay is introduced, effectively ensuring the high bandwidth and dynamic response performance of the force control system. Attached Figure Description

[0026] Figure 1 A schematic diagram of a flexible wheel for attaching three strain gauges;

[0027] Figure 2 This is a block diagram of the amplifier circuit and the summation circuit for weighted summation.

[0028] Figure 3 The curve showing the relationship between the sensor output signal and the load torque when three strain gauges are attached;

[0029] Figure 4 To paste the error analysis diagram under the three strain gauges;

[0030] Figure 5 To paste the error analysis diagram under five strain gauges. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, so as to make the technical solution of the present invention easier to understand and master. In the embodiments, it should be understood that the terms "middle," "upper," "lower," "top," "right side," "left end," "above," "back," "center," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, unless otherwise specified in this specific embodiment, the connection or fixing method between components can be achieved by bolt fixing, pin fixing, or pin connection commonly used in the prior art, etc., and therefore will not be described in detail in this embodiment.

[0032] Example 1

[0033] A method for measuring the built-in torque of a harmonic reducer based on independent gain adjustment includes the following steps;

[0034] Step 1, see Figure 1 M strain gauges are arranged on the diaphragm surface of the flexure of the harmonic reducer; the number of strain gauges M is odd and satisfies M≥2N+1, where N is the highest order of the frequency component of the ripple interference signal to be compensated.

[0035] The number of strain gauges M is at least 3, used to compensate for the fundamental frequency component of the ripple signal. When M=3, three strain gauges are arranged circumferentially on the surface of the flexure diaphragm, and the positional interval of the strain gauges corresponds to one-third of the fundamental frequency period of the ripple signal; or they are arranged symmetrically on opposite sides of the flexure (see the two positions of strain gauge R2 in 1).

[0036] The strain gauge is attached to the inner or outer side of the flexible diaphragm portion; preferably, the strain gauge is attached to the inner side of the flexible diaphragm portion near the hub, and the lead wire is fixed to the stationary hub to improve the durability of the sensor under long-term operation.

[0037] Step 2, see Figure 2 Each strain gauge is equipped with an independent signal amplification channel, and each signal amplification channel has a corresponding adjustable gain coefficient. ;

[0038] Step 3: During the operation of the harmonic reducer, the original output signal of each strain gauge is collected synchronously;

[0039] Step 4: Based on the original output signal, adjust the gain coefficient of the corresponding signal amplification channel. This ensures that the periodic ripple components related to the rotation of the harmonic reducer in the output signal of each strain gauge after gain adjustment cancel each other out after weighted summation, thereby minimizing the output of the total ripple signal; regarding the gain coefficient The determination method provided in this embodiment is a "deterministic method" and a "heuristic method". The "deterministic method" requires Fourier transform of the signal, while the "heuristic method" does not require Fourier transform of the signal.

[0040] The specific details regarding "deterministic methods" are as follows:

[0041] Establish the amplitude of the ripple signal and phase The homogeneous linear equation system:

[0042] ;

[0043] in, m is the gear design coefficient. The input shaft rotation angle is used; the amplitude and phase of each strain gauge signal are obtained through Fourier transform, one of the gain values ​​is preset (e.g., the Mth gain is set to 1), the equations are solved to obtain the relative values ​​of the remaining gains, and finally all gains are adjusted by scaling factors to match the required torque sensitivity.

[0044] The scaling factor is calculated based on the ratio of a known standard torque to a synthesized voltage value. The synthesized voltage value is obtained by weighted summing of the static output signals of each strain gauge and the relative gain value obtained from the "ripple suppression configuration." Essentially, this process calibrates the system using a known torque, converting the voltage signal into a torque quantity, consistent with common sensor calibration methods (such as calibrating a load cell using a standard weight). Specifically, after completing the ripple suppression configuration, a known standard torque is applied to the output of the harmonic reducer, and the static output signals of each strain gauge are recorded. These static output signals are then substituted into the relative gain value obtained from the current "homogeneous linear equations of ripple signal amplitude and phase" to calculate the corresponding synthesized voltage value. The scaling factor is then defined as the standard torque divided by the synthesized voltage value. Finally, the actual gain of each channel is set as the relative gain value multiplied by the scaling factor.

[0045] The details regarding "heuristic methods" are as follows:

[0046] The output signals of all strain gauges after gain adjustment are weighted and summed to obtain the composite signal; the peak value of the composite signal is monitored during the operation of the harmonic reducer; the gain of each channel is finely adjusted (either manually or through a computer algorithm) until the ripple amplitude in the composite signal reaches its minimum.

[0047] It is worth noting that the "heuristic method" does not require establishing a mathematical model or performing a Fourier transform. Instead, it directly optimizes the synthesized signal through experimental fine-tuning. Its core logic is consistent with the "deterministic method"—both use gain adjustment to make the ripple components cancel each other out in the synthesized signal. The only difference between the two methods lies in the implementation path, but the essential nature of the synthesized signal as a "quantitative indicator of the ripple cancellation effect" remains unchanged.

[0048] Step 5: Sum the output signals of all signal amplification channels after gain adjustment as the final torque measurement value.

[0049] In addition, based on the aforementioned method for measuring the built-in torque of a harmonic reducer, this embodiment also discloses a torque sensor system for a harmonic reducer, specifically including a harmonic reducer body; and multiple strain gauges attached to the flexible diaphragm portion (see...). Figure 1 ); and the multi-channel analog amplifier circuit corresponding to each strain gauge (see Figure 2 Each channel has an independently adjustable gain; a summing circuit for weighted summation of the output signals of all signal amplification channels (see [link]). Figure 2 The output of the summing circuit provides a ripple-compensated torque measurement signal.

[0050] Example 2

[0051] This embodiment describes the application of the built-in torque measurement method of the harmonic reducer in Embodiment 1, which involves attaching three strain gauges to the flexural diaphragm portion of the harmonic reducer.

[0052] Three strain gauges are arranged on the diaphragm surface of the flexure in the harmonic reducer. According to theoretical calculations, the three strain gauges can completely compensate for the fundamental frequency component of the ripple. Considering that the period of the fundamental frequency component corresponds to half a rotation of the input shaft, the strain gauges should be distributed at 60-degree intervals within a 180-degree range of the flexure.

[0053] Deterministic methods are used to determine the gain coefficient:

[0054] First, the output of each strain gauge was measured under no-load operation, and FFT analysis was performed to extract the amplitude of the ripple fundamental frequency. and phase .

[0055] Establish a system of equations:

[0056] ;

[0057] ;

[0058] set up Solve and The relative value is then scaled uniformly according to the required sensitivity.

[0059] For experimental results, see Figure 3 The relationship curve between the sensor output signal and the load torque shows that the linearity is good and the hysteresis is minimal under this configuration.

[0060] Example 3

[0061] This embodiment describes the application of the built-in torque measurement method of the harmonic reducer in Embodiment 1, which involves attaching five strain gauges to the flexural diaphragm portion of the harmonic reducer.

[0062] Five strain gauges are arranged on the diaphragm surface of the flexure of the harmonic reducer; to obtain higher precision, the five strain gauges are attached to the flexure at 72-degree intervals.

[0063] A heuristic approach is used to determine the gain coefficients: the system is connected to a computer, which reads the total output signal. A search algorithm is used to fine-tune the gains of the five amplifiers, with the objective function being to minimize the peak value of the total output signal.

[0064] For experimental results, see Figure 4 , Figure 5 It can be seen that compared with three strain gauges, the five strain gauge configuration further reduces the ripple amplitude, with an error of less than ±0.5% over the entire range, and is not significantly affected by the load size.

[0065] Of course, the above are just typical examples of the present invention. In addition, the present invention may have many other specific embodiments. All technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed by the present invention.

Claims

1. A method for measuring the built-in torque of a harmonic reducer based on independent gain adjustment, characterized in that, Includes the following steps; Step 1: Arrange M strain gauges on the diaphragm surface of the flexure of the harmonic reducer; Step 2: Configure an independent signal amplification channel for each strain gauge, with each signal amplification channel having a corresponding adjustable gain coefficient. , ; Step 3: During the operation of the harmonic reducer, the original output signal of each strain gauge is collected synchronously; Step 4: Based on the original output signal, adjust the gain coefficient of the corresponding signal amplification channel. This ensures that the periodic ripple components related to the rotation of the harmonic reducer in the output signal of each strain gauge after gain adjustment cancel each other out after weighted summation, thereby minimizing the output of the total ripple signal. Step 5: Sum the output signals of all signal amplification channels after gain adjustment as the final torque measurement value; The number M of strain gauges satisfies M≥2N+1, where N is the highest order of the frequency component of the ripple interference signal to be compensated. In step 4, the gain coefficient is determined. The method employs a "deterministic approach," and step 4 includes: Establish the amplitude of the ripple signal and phase The homogeneous linear equation system: ； in, m is the gear design coefficient. Input axis rotation angle; The amplitude and phase of each strain gauge signal are obtained through Fourier transform. One gain value is preset, and the relative values ​​of the remaining gains are obtained by solving the system of equations. Finally, all gains are adjusted by a scaling factor to match the required torque sensitivity. The scaling factor is calculated based on the ratio of the known standard torque to the synthesized voltage value. The synthesized voltage value is obtained by weighted summing of the relative gain values ​​obtained by the static output signals of each strain gauge and the ripple suppression configuration. The scaling factor is defined as the known standard torque divided by the synthesized voltage value. Finally, the actual gain of each signal amplification channel is set to the relative gain value multiplied by the scaling factor.

2. The method for measuring the built-in torque of a harmonic reducer as described in claim 1, characterized in that, The number M of strain gauges is an odd number.

3. The method for measuring the built-in torque of a harmonic reducer as described in claim 2, characterized in that, The number of strain gauges M is at least 3, used to compensate for the fundamental frequency component of the ripple signal.

4. The method for measuring the built-in torque of a harmonic reducer as described in claim 3, characterized in that, When M=3, three strain gauges are arranged circumferentially on the surface of the flexure diaphragm, and the positional interval of the strain gauges corresponds to one-third of the fundamental frequency period of the ripple signal; or the strain gauges are arranged symmetrically on opposite sides of the flexure.

5. The method for measuring the built-in torque of a harmonic reducer as described in claim 4, characterized in that, The strain gauge is attached to the inner or outer side of the flexible diaphragm portion.

6. The method for measuring the built-in torque of a harmonic reducer as described in claim 5, characterized in that, The strain gauge is attached to the inner side of the flexible diaphragm near the hub, and the lead wire is fixed to the stationary hub to improve the durability of the sensor under long-term operation.

7. A harmonic reducer torque sensor system applying the harmonic reducer built-in torque measurement method as described in any one of claims 1 to 6, characterized in that, include: Harmonic reducer body; Multiple strain gauges are attached to the flexible diaphragm section; Each strain gauge has a corresponding signal amplification channel, and each signal amplification channel has an independently adjustable gain coefficient; A summation circuit used to perform weighted summation of the output signals of all signal amplification channels; The output of the summing circuit provides a ripple-compensated torque measurement signal.

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