Membrane-beam type six-dimensional force sensor with overload structure and fault-tolerant measurement method thereof

Abstract

The application relates to a membrane-beam type six-dimensional force sensor with an overload structure and a fault-tolerant measurement method thereof. The six-dimensional force sensor comprises a protective base, a membrane-beam type elastic body mounted on the protective base and a protective end cover covering the outer side of one end of the membrane-beam type elastic body; and a cross protection block is mounted in the membrane-beam type elastic body. The application provides a membrane-beam type six-dimensional force sensor structure, a cross type overload protection mechanism is designed and arranged in the interior of the sensor, the overload protection capability of the six-dimensional force sensor in the Mx direction and the My direction is improved under the condition of the same outer diameter size, and the overall overload resistance capability of the six-dimensional force sensor is improved. The application provides a BPNN sensor fault-tolerant measurement method based on a genetic algorithm optimization, the method can predict the damaged one-dimensional measurement signal through the remaining five dimensions under the condition that a certain dimension signal of the six-dimensional force sensor is damaged, the accurate measurement of the six-dimensional force sensor is realized, and the fault-tolerant capability and the measurement reliability of the six-dimensional force sensor are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of six-dimensional force sensor measurement, in particular to a membrane-beam type six-dimensional force sensor with an overload structure and a fault-tolerant measurement method thereof. BACKGROUND

[0002] As one of the key components of a smart manipulator, a six-dimensional force sensor can assist the manipulator to obtain three-dimensional force and three-dimensional torque information at the end, and realize automatic force feedback control at the end of the manipulator, so as to better perform end operation tasks.

[0003] In order to ensure the working performance of a space engine, the interior of the space engine needs to be detected. Since the inspection port of some models of space engines is small in diameter (for example, Φ74mm), a person cannot directly perform relevant operations, and it is a feasible scheme to use a smart manipulator to enter the interior of the engine for operation. The wrist of the smart manipulator is provided with a six-dimensional force sensor, and the end is provided with a dexterous gripper, which is loaded with lighting and camera equipment and the like. These equipment themselves increase the load of the six-dimensional force sensor, especially when the manipulator is in a horizontal state. If the smart manipulator collides, makes an operation mistake or has a large vibration during operation, the six-dimensional force sensor is more likely to be damaged in the Mx and My directions. Therefore, it is required that the outer diameter of the six-dimensional force sensor installed on the wrist of the smart manipulator is smaller than the size of the inspection port, and the six-dimensional force sensor has a high overload capacity in the Mx and My directions. Moreover, due to the particularity of the space environment, if damage occurs, the sensor cannot be repaired. Therefore, in order to improve the use reliability of the six-dimensional force sensor, it is required that the six-dimensional force sensor still has a measurement capacity in the case of damage in a certain dimension, that is, the six-dimensional force sensor has a certain fault-tolerant measurement capacity.

[0004] At present, some six-dimensional force sensors with overload protection mechanisms have appeared in the prior art, but they have a relatively weak overload capacity in the Mx and My directions than in other directions, and do not have fault-tolerant measurement capacity, and are not suitable for special space environments. SUMMARY

[0005] In order to solve the problems in the prior art, the present application provides a membrane-beam type six-dimensional force sensor with an overload structure and a fault-tolerant measurement method thereof.

[0006] To achieve the above object, the present application adopts the following technical scheme:

[0007] In a first aspect of the present application, a membrane-beam type six-dimensional force sensor with an overload structure is disclosed, which comprises:

[0008] The protection base, the membrane-beam elastic body installed on the protection base, and the protection end cover covering the outside of one end of the membrane-beam elastic body; the membrane-beam elastic body is installed with a cross protection block.

[0009] Further, the membrane-beam elastic body comprises an elastic body main body formed by a loading ring, an annular diaphragm and a fixing ring arranged coaxially in sequence, and a force transmission column embedded in the middle of the elastic body main body; the force transmission column is connected with the elastic body main body through several rectangular beams; the loading ring, the rectangular beam, the force transmission column, the annular diaphragm and the fixing ring are integrally formed;

[0010] The cross protection block is embedded and installed in the inside of the upper end of the elastic main body and above the force transmission column and the rectangular beam;

[0011] The loading ring is provided with several uniformly distributed end cover fixing screw holes, sector-shaped bosses and sector-shaped grooves;

[0012] The sector-shaped boss is provided with a loading screw hole;

[0013] The force transmission column is provided with several lead holes and a middle through hole;

[0014] The fixing ring is provided with several uniformly distributed connection fixing holes on the side surface, and the fixing ring bottom step is provided with several bottom cover fixing holes;

[0015] Further, the number of the rectangular beams is four, which are a first rectangular beam, a second rectangular beam, a third rectangular beam and a fourth rectangular beam;

[0016] The rectangular beams are uniformly distributed along the outer periphery of the force transmission column;

[0017] Three groups of strain gauges are attached to the four rectangular beams, each group having four pieces, forming a first Wheatstone full bridge circuit; the first Wheatstone full bridge circuit is used for measuring X-direction torque, Y-direction torque and Z-direction torque;

[0018] The strain gauges for measuring X-direction torque, i.e. Mx, are R1, R2, R3 and R4, wherein R1 and R2 are respectively attached to the upper surfaces of the first rectangular beam along the radial central symmetry axis and close to the edge positions of the two ends, R3 and R4 are respectively attached to the upper surfaces of the third rectangular beam along the radial central symmetry axis and close to the edge positions of the two ends, and R1, R2, R3 and R4 constitute a Wheatstone full bridge circuit I;

[0019] The strain gauges for measuring the Y-direction torque, namely My, are R5, R6, R7 and R8, wherein R5 and R6 are respectively attached to the upper surface of the second rectangular beam along the radial central symmetry axis and close to the two end edges, and R7 and R8 are respectively attached to the upper surface of the fourth rectangular beam along the radial central symmetry axis and close to the two end edges, and R5, R6, R7 and R8 constitute a Wheatstone full bridge circuit II;

[0020] The strain gauges for measuring the Z-direction torque, namely Mz, are R9, R10, R11 and R12, wherein R9 and R10 are respectively attached to the two side surfaces of the first rectangular beam along the radial central symmetry axis and close to the inner end edges, and R11 and R12 are respectively attached to the two side surfaces of the third rectangular beam along the radial central symmetry axis and close to the inner end edges, or R9 and R10 are respectively attached to the two side surfaces of the second rectangular beam along the radial central symmetry axis and close to the inner end edges, and R11 and R12 are respectively attached to the two side surfaces of the fourth rectangular beam along the radial central symmetry axis and close to the inner end edges, and R9, R10, R11 and R12 constitute a Wheatstone full bridge circuit III.

[0021] The four rectangular beams are of the same size, and are located between the loading ring and the force transmission column; the upper end surface of the loading ring is higher than the upper end surface of the force transmission column by at least 2 mm; the upper end surface of the force transmission column is higher than the upper surface of the rectangular beam by at least 1 mm; the annular diaphragm is located between the fixed ring and the force transmission column, and at the lower end of the force transmission column, the lower end surface of the force transmission column is higher than the lower end surface of the annular diaphragm by at least 1 mm; there is a gap between the lower end surface of the four rectangular beams and the upper end surface of the annular diaphragm.

[0022] Further, three groups of strain gauges are attached to the annular diaphragm, each group having four strain gauges, constituting a second Wheatstone full bridge circuit; the second Wheatstone full bridge circuit is used for measuring the X-direction force, the Y-direction force and the Z-direction force;

[0023] The strain gauges for measuring the X-direction force, namely Fx, are R13, R14, R15 and R16, constituting a Wheatstone full bridge circuit IV, and are respectively attached along the X-axis direction of the annular diaphragm;

[0024] The strain gauges for measuring the Y-direction force, namely Fy, are R17, R18, R19 and R20, constituting a Wheatstone full bridge circuit V, and are respectively attached along the Y-axis direction of the annular diaphragm;

[0025] The strain gauges for measuring the Z-direction force, namely Fz, are R21, R22, R23 and R24, constituting a Wheatstone full bridge circuit VI, and are respectively attached along the diameter direction of the annular diaphragm which is rotated by 45° from the Y-axis or the Z-axis; the strain gauges in the Fx, Fy and Fz directions are all attached close to the outer diameter and the inner diameter of the annular diaphragm.

[0026] Further, the protective end cover comprises a circular flat plate and a circular ring column sleeved outside the circular flat plate; the circular flat plate is integrally formed with the circular ring column;

[0027] The circular flat plate is provided with a plurality of counterbores and a plurality of fan-shaped holes distributed along the circumference; the lower surface of the circular flat plate is provided with a circular groove;

[0028] The counterbores on the protective end cover are fixedly connected with the end cover fixing screw holes on the loading ring through screws;

[0029] The fan-shaped holes are matched and installed with the fan-shaped bosses, and the fan-shaped bosses are higher than or equal to the circular flat plate.

[0030] Further, the protective base comprises a bottom plate and first and second bosses sequentially arranged above the bottom plate; the first and second bosses form a stepped surface;

[0031] The bottom plate is provided with a plurality of counterbores, and a groove is arranged in the middle of the bottom plate;

[0032] The side edge of the first boss is provided with a cable outlet hole;

[0033] The second boss is provided with a plurality of threaded holes and pin holes;

[0034] The bottom plate, the first boss and the second boss are integrally formed;

[0035] The counterbores and the bottom cover fixing holes are fixedly connected through screws.

[0036] Further, the annular diaphragm and the fixing ring form a planar step and a side step;

[0037] The bottom surface and the inner surface of the circular ring column are gap-fitted with the planar step and the side step, respectively;

[0038] The upper end surface of the force transmission column is gap-fitted with the lower end surface of the circular plate, and the lower end surface of the force transmission column is gap-fitted with the stepped surface;

[0039] Further, the cross-shaped protective block comprises a circular plate and four fan-shaped rectangular beams of the same size arranged along the circular plate; the fan-shaped rectangular beams and the circular plate are an integral structure; the four fan-shaped rectangular beams are respectively a first fan-shaped rectangular beam, a second fan-shaped rectangular beam, a third fan-shaped rectangular beam and a fourth fan-shaped rectangular beam; the four fan-shaped rectangular beams are vertically distributed along the circumference of the circular plate to form a cross-shaped structure;

[0040] The circular plate is provided with a plurality of counterbores, the reverse surface of the circular plate is provided with a boss, and the boss is provided with a pin column;

[0041] The cross-shaped protective block is fixedly connected with the protective base through threads.

[0042] Each fan-shaped rectangular beam comprises a fan-shaped block and a rectangular block arranged in sequence, the fan-shaped block is arranged in the cavity formed between the fan-shaped groove and the groove, the fan-shaped block and the fan-shaped groove are gap-fitted, and left-right gap a, radial gap b and up-down gap c are formed between the fan-shaped block and the fan-shaped groove, wherein the left-right gap a is used for overload protection in the Mz direction, the radial gap b is used for overload protection in the Fx / Fy direction, and the up-down gap c is used for overload protection in the Mx / My direction.

[0043] In the second aspect of the application, a fault-tolerant measurement method of the above-mentioned six-dimensional force sensor is disclosed, and the method comprises:

[0044] S1, calibrating the film-beam six-dimensional force sensor to obtain each-dimensional output voltage data set;

[0045] S2, establishing a BPNN neural network model, taking five-dimensional output voltage data of the six-dimensional force sensor as input and taking output voltage data of the fault dimension as output;

[0046] S3, optimizing and training the BPNN neural network model by using a genetic algorithm to obtain optimal weights and thresholds;

[0047] S4, putting the data into the trained BPNN neural network model, predicting and outputting the signal of the fault dimension by using the trained BPNN neural network model, and performing fault-tolerant measurement.

[0048] Further, the calibrated film-beam six-dimensional force sensor obtains each-dimensional output voltage data set, comprising:

[0049] Adjusting the calibration platform, fixing the film-beam sensor on the calibration platform by bolts, and installing a loading cap on the top thereof, calibrating the zero baseline of the output voltage of the six-dimensional force sensor in each direction, gradually increasing the load to the full range according to the divided loading points in the positive / negative direction of each dimension of the six-dimensional force sensor, then gradually reducing the load to zero, recording the output voltage value, and dividing the obtained each-dimensional output voltage data set into two parts of training set and test set according to the ratio of 7:3;

[0050] The BPNN neural network model is established, five-dimensional output voltage data of the six-dimensional force sensor are taken as input, and output voltage data of the fault dimension are taken as output, comprising:

[0051] The arbitrary five-dimensional output voltage data is taken as the input of the input layer of the BPNN neural network model, the remaining one-dimensional output voltage data is taken as the output of the output layer of the BPNN neural network model, two hidden layers are further included, the number of neurons of the hidden layer of the BPNN neural network model is set to 10 according to an experience formula l = (n + m) ^ (1 / 2) + a, the activation function is set to sigmoid(), and a loss function suitable for a regression problem is set according to experience, wherein n is the number of neurons of the input layer, m is the number of neurons of the output layer, and a is a constant between [1, 10];

[0052] The BPNN neural network model is optimized and trained by using the genetic algorithm to obtain optimal weights and thresholds, and the method comprises the following steps:

[0053] All the weights and thresholds are integrated into a chromosome, a plurality of different chromosomes are randomly generated, the optimal chromosome is obtained through selection, crossover and mutation, the fitness function is used to evaluate the advantages and disadvantages of the chromosome, the optimal set of weights and thresholds is obtained, the optimal weights and thresholds are substituted into the BPNN neural network model, the evolution number, population size, crossover probability and mutation probability of the genetic algorithm are set, the iteration number, error threshold and learning rate of the BPNN neural network model are set, all the data are normalized, a mapping relationship between five dimensions and one dimension is fitted by using test set data, and the trained BPNN neural network model is verified by using the test set.

[0054] The data is put into the trained BPNN neural network model, the trained BPNN neural network model is used to predict and output a fault dimension signal, and fault-tolerant measurement is performed, and the method comprises the following steps:

[0055] The five-dimensional voltage output signal of the six-dimensional force sensor with a one-dimensional fault is put into the trained BPNN neural network model, the six-dimensional force sensor signal is predicted by using the five-dimensional sensor signal, complete six-dimensional measurement data are obtained, and fault-tolerant measurement of the sensor is realized.

[0056] Compared with the prior art, the method has the following advantages:

[0057] (1) The application provides a membrane-beam type six-dimensional force sensor structure, a cross type overload protection mechanism is designed and arranged in the interior of the sensor, the overload protection capability of the six-dimensional force sensor in the Mx direction and the My direction is improved under the condition of the same outer diameter size and range, and thus the overall overload protection capability of the six-dimensional force sensor is improved. The application innovatively provides a membrane-beam type six-dimensional force sensor, and a cross type overload protection mechanism is arranged in the interior of the sensor, the addition of the overload mechanism outside the sensor is avoided, the outer diameter of the sensor is increased, the overload protection capability of the sensor in the Mx direction and the My direction is improved under the condition of the same outer diameter and range, and thus the overall overload protection capability of the six-dimensional force sensor is improved. The six-dimensional force sensor has the characteristics of high precision, compact structure and easy processing, and meets the detection requirements of the space environment, the mechanical arm maintenance small caliber (Φ74mm) and the space engine.

[0058] (2) The application provides a BPNN sensor fault-tolerant measurement method based on a genetic algorithm optimization, the method can realize accurate measurement of the six-dimensional force sensor under the condition that one-dimensional measurement signals of the six-dimensional force sensor are damaged, the remaining five dimensions are used to predict the damaged one-dimensional measurement signals, and the accurate measurement of the six-dimensional force sensor is realized. The application innovatively provides a fault-tolerant measurement method, avoids the complexity of manual disassembly and maintenance when the measurement circuit is damaged, saves manpower and material resources, the network can quickly predict complete measurement data, reduces the time cost, and overall improves the fault-tolerant capability and measurement reliability of the six-dimensional force sensor. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 It is a structure schematic view of the six-dimensional force sensor in the application;

[0060] Figure 2 It is an explosion structure schematic view of the six-dimensional force sensor in the application;

[0061] Figure 3 It is a structure schematic view of the membrane-beam type elastic body;

[0062] Figure 4 It is a structure schematic view of the protection end cover;

[0063] Figure 5 It is a structure schematic view of the protection base;

[0064] Figure 6 It is a structure schematic view of the cross protection block;

[0065] Figure 7 It is a longitudinal sectional view of the application;

[0066] Figure 8 It is Figure 7 the E point enlarged view in the application;

[0067] Figure 9 yes Figure 7 Enlarged view of point F;

[0068] Figure 10 yes Figure 7 Enlarged view of point G in the middle;

[0069] Figure 11 This is a top view of the assembly of the protective cross block and the elastomer;

[0070] Figure 12 yes Figure 10 Enlarged view of point E in the middle;

[0071] Figure 13 This is a schematic diagram of the upper layer patch of the sensor;

[0072] Figure 14 This is a schematic diagram of the lower layer patch of the sensor;

[0073] Figure 15 This is a schematic diagram of the sensor's six-directional bridge configuration;

[0074] Figure 16 This is a schematic diagram of the fault-tolerant measurement method in this invention. Detailed Implementation

[0075] The present invention will be further described below with reference to the accompanying drawings:

[0076] like Figure 1 and Figure 2 The diagram shows a membrane-beam type six-dimensional force sensor with an overload structure. The six-dimensional force sensor includes a protective end cap 1, a cross-shaped protective block 2, a membrane-beam type six-dimensional force sensor elastomer 3, and a protective base 4.

[0077] like Figure 3 , Figure 13 and Figure 14As shown, the membrane-beam six-dimensional force sensor elastomer 3 is a force measurement module, including a loading ring 31, rectangular beams (321, 322, 323 and 324), a force transmission column 33, a ring-shaped diaphragm 34 and a fixing ring 35. This design can reduce the overall outer diameter size of the sensor, and in the case of the same outer diameter size, the center of the sensor has a relatively large through hole, which is convenient for wiring or mounting connecting components, etc. The loading ring is uniformly distributed with a plurality of end cap fixing screw holes 311, a fan-shaped boss 312 and a fan-shaped groove 314. The fan-shaped boss 312 is provided with a loading screw hole 313, and the external load can be directly loaded through the loading screw hole 313, reducing the load through the adapter plate and thereby reducing the external load loss. The rectangular beams (321, 322, 323 and 324) are uniformly distributed along the circumference and are attached with three groups of strain gauges, each group having four pieces, forming a Wheatstone full bridge circuit, which bears the measurement of X-direction torque, Y-direction torque and Z-direction torque. The force transmission column 33 has a plurality of lead holes 331 and a middle through hole 332. The ring-shaped diaphragm 34 is attached with three groups of strain gauges, each group having four pieces, forming a Wheatstone full bridge circuit, which bears the measurement of X-direction force, Y-direction force and Z-direction force. The fixing ring 35 is uniformly distributed with a plurality of connecting fixing holes 351 on the side surface, which facilitates the disassembly of the sensor and the external connecting base during use. A plurality of bottom cover fixing holes are provided on the bottom step of the fixing ring 35. The loading ring 31, the rectangular beams (321, 322, 323 and 324), the force transmission column 33, the ring-shaped diaphragm 34 and the fixing ring 35 are of an integrated structure.

[0078] As shown in Figure 4 The protection end cover 1 includes a circular flat plate 11 and a circular ring column 12. The circular ring flat plate 11 has a plurality of sink holes 111 and fan-shaped holes 112 distributed along the circumference. The lower surface of the circular ring flat plate 11 has a circular groove 113. The circular flat plate 11 and the circular ring column 12 are of an integrated structure. The sink hole 13 on the protection end cover 1 is fixedly connected with the end cap fixing screw hole 311 on the loading ring 31 through a screw. The fan-shaped hole 112 is installed in cooperation with the fan-shaped boss 312. The height of the fan-shaped boss 312 is higher than or equal to that of the circular flat plate 11.

[0079] As shown in Figure 5 The protection base 4 includes a circular plate 41, a large boss 42 and a small boss 43. The circular plate 41 is distributed with a plurality of sink holes 411. The circular plate has a groove in the middle. The large boss 42 has a cable outlet hole 421 on the side edge. The small boss has a plurality of screw holes 431 and pin holes 432. The circular plate 41, the large boss 42 and the small boss 43 are of an integrated structure. The sink hole 411 on the protection base 4 is fixedly connected with the bottom cover fixing hole on the fixing ring 35 of the membrane-beam six-dimensional force elastomer 3 through a screw.

[0080] As shown in Figure 6As shown in the drawings, the cross protection block 2 comprises four identical size fan rectangular beams (21, 22, 23 and 24) and a circular plate 25, the fan rectangular beam 21 is composed of a fan block 211 and a rectangular block 212, the fan rectangular beams (21, 22, 23 and 24) are vertically distributed along the circumference of the circular plate 25 to form a "cross" structure, the circular plate 25 is provided with a plurality of counterbores 251, the reverse side of the circular plate 25 is provided with a boss 26, the boss is provided with a pin 27 for positioning during installation; the fan rectangular beams (21, 22, 23 and 24) and the circular plate 25 are an integral structure, the cross protection block 2 is fixedly connected with the protection base 4 through threads.

[0081] As shown in the drawings, Figure 7 , Figure 8 , Figure 11 and Figure 12 As shown in the drawings, the fan block 211 on the cross protection block 2 is placed in the cavity formed between the fan-shaped groove 314 and the groove 113, the fan block 21 and the fan-shaped groove 314 are gap-fitted, the fan block 21 and the fan-shaped groove 314 form left and right gaps a, radial gaps b and upper and lower gaps c, wherein the left and right gaps a are mainly used for overload protection in the Mz direction, the radial gaps b are mainly used for overload protection in the Fx / Fy direction, and the upper and lower gaps c are mainly used for overload protection in the Mx / My direction.

[0082] As shown in the drawings, Figure 7 and Figure 9 As shown in the drawings, the bottom surface and the inner surface of the circular ring column 12 are gap-fitted with the flat step 352 and the side step 353 respectively, so as to prevent the safe deformation of the sensor from being blocked.

[0083] As shown in the drawings, Figure 7 and Figure 10 As shown in the drawings, the upper end surface of the force transmission column 33 is gap-fitted with the lower end surface of the circular plate 25, and the lower end surface of the force transmission column 33 is gap-fitted with the step surface 422, so as to prevent the safe deformation of the sensor from being blocked.

[0084] As shown in the drawings, Figure 3As shown, the four rectangular beams (321, 322, 323 and 324) are completely consistent in size, and are located between the loading ring 31 and the force transmission column 33. The upper end surface of the loading ring 31 is higher than the upper end surface of the force transmission column 33 by at least 2 mm, and the upper end surface of the force transmission column 33 is higher than the upper surfaces of the four rectangular beams (321, 322, 323 and 324) by at least 1 mm, thereby protecting the bonded strain gauges and preventing damage caused by touching. The annular diaphragm 34 is located between the fixing ring 35 and the force transmission column 33, and at the lower end of the force transmission column 33. The lower end surface of the force transmission column 33 is higher than the lower end surface of the annular diaphragm 34 by at least 1 mm, thereby protecting the bonded strain gauges and preventing damage caused by touching. There is a gap between the lower end surfaces of the four rectangular beams (321, 322, 323 and 324) and the upper end surface of the annular diaphragm 34, and the distance of the gap is the minimum distance that does not affect the movement of the sensor.

[0085] As shown in Figure 13 and Figure 15 , the strain gauges for measuring the X-direction moment, i.e. Mx, are R1, R2, R3 and R4, respectively. R1 and R2 are respectively attached to the upper surface of the first rectangular beam 321 along the radial center axis and close to the edge positions of the two ends, and R3 and R4 are respectively attached to the upper surface of the third rectangular beam 323 along the radial center axis and close to the edge positions of the two ends. R1, R2, R3 and R4 constitute a Wheatstone full bridge circuit I. The strain gauges for measuring the Y-direction moment, i.e. My, are R5, R6, R7 and R8, respectively. R5 and R6 are respectively attached to the upper surface of the second rectangular beam 322 along the radial center axis and close to the edge positions of the two ends, and R7 and R8 are respectively attached to the upper surface of the fourth rectangular beam 324 along the radial center axis and close to the edge positions of the two ends. R5, R6, R7 and R8 constitute a Wheatstone full bridge circuit II. The strain gauges for measuring the Z-direction moment, i.e. Mz, are R9, R10, R11 and R12, respectively. R9 and R10 are respectively attached to the two side surfaces of the first rectangular beam 321 along the radial center axis and close to the edge positions of the inner ends, or R9 and R10 are respectively attached to the two side surfaces of the second rectangular beam 322 along the radial center axis and close to the edge positions of the inner ends. R11 and R12 are respectively attached to the two side surfaces of the third rectangular beam 323 along the radial center axis and close to the edge positions of the inner ends, or R11 and R12 are respectively attached to the two side surfaces of the fourth rectangular beam 324 along the radial center axis and close to the edge positions of the inner ends. R9, R10, R11 and R12 constitute a Wheatstone full bridge circuit III.

[0086] As shown in Figure 14 and Figure 15As shown, the strain gauges R13, R14, R15 and R16 for measuring the X-direction force Fx constitute a Wheatstone full bridge circuit IV and are respectively adhered along the X-axis direction of the annular diaphragm 34; the strain gauges R17, R18, R19 and R20 for measuring the Y-direction force Fy constitute a Wheatstone full bridge circuit V and are respectively adhered along the Y-axis direction of the annular diaphragm 34; the strain gauges R21, R22, R23 and R24 for measuring the Z-direction force Fz constitute a Wheatstone full bridge circuit VI and are respectively adhered along the diameter direction of the annular diaphragm 34 which is rotated by 45° from the Y-axis or the Z-axis; the strain gauges in the Fx, Fy and Fz directions are all adhered at the outer diameter and the inner diameter of the annular diaphragm.

[0087] In order to make the six-dimensional force sensor have fault-tolerant capability, a BPNN sensor fault-tolerant force measurement method based on genetic algorithm optimization is proposed. The method can predict the damaged one-dimensional measurement signal through the remaining five dimensions under the condition that the six-dimensional force sensor is damaged in one dimension, so as to realize accurate measurement of the six-dimensional force sensor. The flow chart of the fault-tolerant measurement method is as shown in Figure 16 The specific steps include the following steps:

[0088] (1) Calibrate the membrane-beam type six-dimensional force sensor and establish the output voltage data set of each dimension: adjust the calibration platform, fix the membrane-beam type sensor on the calibration platform with bolts, and install a loading cap on the top, calibrate the zero baseline of the output voltage of the six-dimensional force sensor in each direction, gradually increase the load to the full range according to the divided loading points in the positive / negative direction of each dimension of the six-dimensional force sensor, then gradually reduce the load to zero, and record the output voltage value, and divide the obtained output voltage data set of each dimension into two parts of training set and test set according to the proportion of 7:3.

[0089] (2) Five-dimensional input, one-dimensional output, and establishment of BPNN: take any five-dimensional output voltage data as the input of the input layer of the BPNN, and take the remaining one-dimensional output voltage data as the output of the output layer, and include two hidden layers, set the number of neurons of the hidden layer to 10 according to the empirical formula l=(n+m)^(1 / 2)+a (n is the number of input layer neurons, m is the number of output layer neurons, and a is a constant between [1, 10]), set the activation function to sigmoid(), and set the loss function suitable for regression problems according to experience.

[0090] (3) Using genetic algorithm to obtain the optimal weight and threshold, optimizing BPNN: the weight and threshold of BPNN are randomly initialized, thus leading to unstable and unsatisfactory effect of neural network, in addition, BPNN always descends along the direction of negative gradient, leading to that BP network is easily trapped in local minimum value and unable to obtain global optimal solution. The core idea of genetic algorithm is Darwin's biological evolution theory-"survival of the fittest", the algorithm integrates all the weight and threshold into a chromosome, then randomly generates different groups of chromosomes, obtains the optimal chromosome through selection, crossover and mutation, wherein the fitness function is used to evaluate the advantages and disadvantages of the chromosome, that is, to obtain the optimal weight and threshold, then the optimal weight and threshold are substituted into BPNN, the evolution number, population size, crossover probability and mutation probability of genetic algorithm are set, and the iteration number, error threshold and learning rate of BPNN are set. The whole data is normalized, a five-dimensional and one-dimensional mapping relationship is fitted by using test set data, and the effect of the trained network is verified by using test set.

[0091] (4) Bringing in fault data, using the trained BPNN to predict signal prediction, realizing fault-tolerant measurement: the five-dimensional voltage output signal of the film-beam six-dimensional force sensor with one-dimensional circuit fault is put into the trained network, the sixth dimension signal is predicted by the five-dimensional sensor signal, so that the complete six-dimensional measurement data is obtained, and the fault-tolerant measurement of the sensor is realized.

[0092] Tables 1-6 respectively show the prediction results of the fault-tolerant method proposed in the application when facing any one-dimensional circuit fault, and from the tables, it can be seen that the prediction errors of fx, fy, fz, mx, my and mz are 0.225%, 0.640%, 0.431%, 2.73%, 0.190% and 0.82% respectively, all of which meet the accuracy requirements in use. Compared with the fault sensor without using the measurement method, no matter which one-dimensional measurement circuit is faulty, the complete and accurate six-dimensional measurement data can be obtained by using the fault-tolerant method proposed in the application, and the results show that the method has good effect and great use value in processing the fault of film-beam six-dimensional force sensor.

[0093] Table 1 shows the prediction result example of fx direction

[0094] Sequence number Umx Umy Umz Ufy Ufz Ufx (true value) Ufx (predicted value) 1 0 -779 15 1 -41 -809 -808.85 2 0 -57 -46 7 -9 -107 -107.11 3 -25 -10 -12 56 -3 -3 -3.017

[0095] Table 2 shows the prediction result example of fy direction

[0096] Sequence number Umz Ufx Umx Umy Ufz Ufy (true value) Ufy (predicted value) 1 -34 -56 -2 -34 -4 7 6.9185 2 16 -808 1 -779 -39 2 2.0144 3 -28 -3 19 -9 3 -41 -41.015

[0097] Table 3 shows the prediction result example of fz direction

[0098] Sequence number Umz Ufx Ufy Umx Ufz Umy (true value) Umy (predicted value) 1 -56 -158 6 1 -79 -13 -13.15 2 -34 -56 7 -1 -34 -4 -4.0567 3 -45 -106 7 0 -57 -9 -8.9988

[0099] Table 4 shows the prediction result example of mx direction

[0100] Sequence number Umz Ufx Ufy Umx Ufz Umy (true value) Umy (predicted value) 1 -34 -56 8 -34 -4 -1 -1.0827 2 -50 3 999 -8 -42 -999 -998.98 3 -20 -3 11 -9 0 -7 -7.0061

[0101] Table 5 Predicted my direction results example

[0102] Sequence number Ufx Ufy Umx Umy Ufz Umz (true value) Umz (predicted value) 1 -44 -4 -138 63 5 -9 -9.0329 2 -57 45 16 -21 1102 43 43.006 3 -21 -4 10 -6 0 -10 -10.057

[0103] Table 6 Predicted mz direction results example

[0104] ​ ​ ​ ​ ​ ​ ​ ​ 1 -4 -241 247 -8 12 -10 -10.016 2 -5 -42 17 -10 1 -34 -34.061 3 -5 -489 493 -9 20 1 1.0114

[0105] The above-described embodiments are merely intended to describe the preferred embodiments of the present application, and are not intended to limit the scope of the present application. Various modifications and improvements of the present application made by those skilled in the art, without departing from the design spirit of the present application, shall fall within the scope of the present application defined by the claims.

Claims

1. A membrane-beam six-dimensional force sensor with an overload structure, characterized by The six-dimensional force sensor comprises: The protection base (4), the membrane-beam elastic body (3) installed on the protection base (4), and the protection end cover (1) covering the outer side of one end of the membrane-beam elastic body (3); the cross protection block (2) is installed in the membrane-beam elastic body (3); The membrane-beam elastic body (3) comprises an elastic body main body formed by sequentially coaxially arranging a loading ring (31), an annular diaphragm (34) and a fixing ring (35), and a force transmission column (33) embedded in the middle of the elastic body main body; the force transmission column (33) is connected with the elastic body main body through a plurality of rectangular beams; the loading ring (31), the rectangular beam, the force transmission column (33), the annular diaphragm (34) and the fixing ring (35) are integrally formed; The cross protection block (2) is embedded and installed in the inner side of the upper end of the elastic body main body and located above the force transmission column (33) and the rectangular beam; The loading ring (31) is provided with a plurality of uniformly distributed end cover fixing screw holes (311), a fan-shaped boss (312) and a fan-shaped groove (314); The fan-shaped boss (312) is provided with a loading screw hole (313); The force transmission column (33) is provided with a plurality of lead hole and middle through hole; The fixing ring (35) is provided with a plurality of uniformly distributed connection fixing holes on the side surface, and a plurality of bottom cover fixing holes are arranged on the bottom step of the fixing ring (35); The cross protection block (2) comprises a circular plate (25) and four fan-shaped rectangular beams of the same size arranged along the circular plate (25); the fan-shaped rectangular beams and the circular plate (25) are an integral structure; the four fan-shaped rectangular beams are respectively a first fan-shaped rectangular beam (21), a second fan-shaped rectangular beam (22), a third fan-shaped rectangular beam (23) and a fourth fan-shaped rectangular beam (24); the four fan-shaped rectangular beams are vertically distributed along the circumference of the circular plate (25) to form a cross-shaped structure; A plurality of counterbores (251) are distributed on the circular plate (25), the reverse surface of the circular plate (25) is provided with a boss (26), and the boss (26) is provided with a pin column (27); The cross protection block (2) and the protection base (4) are fixedly connected through threads; The protection end cover comprises a circular flat plate (11) and a circular ring column (12) sleeved outside the circular flat plate (11); a circular groove (113) is arranged on the lower surface of the circular flat plate (11); Each fan-shaped rectangular beam comprises a fan-shaped block (211) and a rectangular block (212) arranged in sequence, the fan-shaped block (211) is arranged in the cavity formed between the fan-shaped groove (314) and the groove (113), the fan-shaped block (211) and the fan-shaped groove (314) are gap-fitted, the fan-shaped block (211) and the fan-shaped groove (314) form left-right gap a, radial gap b and up-down gap c, wherein the left-right gap a is used for overload protection in the Mz direction, the radial gap b is used for overload protection in the Fx / Fy direction, and the up-down gap c is used for overload protection in the Mx / My direction.

2. The six-dimensional force sensor according to claim 1, wherein The number of the rectangular beams is four, which are a first rectangular beam (321), a second rectangular beam (322), a third rectangular beam (323) and a fourth rectangular beam (324); The rectangular beams are uniformly distributed along the outer periphery of the force transmission column (33); The four rectangular beams are provided with three groups of strain gauges, each group having four strain gauges, to form a first Wheatstone full-bridge circuit; the first Wheatstone full-bridge circuit is used to measure X-direction torque, Y-direction torque and Z-direction torque; The strain gauges for measuring X-direction torque, i.e. Mx, are R1, R2, R3 and R4, wherein R1 and R2 are respectively attached to the upper surface of the first rectangular beam (321) along the radial central symmetry axis and close to the two end edges, R3 and R4 are respectively attached to the upper surface of the third rectangular beam (323) along the radial central symmetry axis and close to the two end edges, and R1, R2, R3 and R4 form a Wheatstone full-bridge circuit I; The strain gauges for measuring Y-direction torque, i.e. My, are R5, R6, R7 and R8, wherein R5 and R6 are respectively attached to the upper surface of the second rectangular beam (322) along the radial central symmetry axis and close to the two end edges, R7 and R8 are respectively attached to the upper surface of the fourth rectangular beam (324) along the radial central symmetry axis and close to the two end edges, and R5, R6, R7 and R8 form a Wheatstone full-bridge circuit II; The strain gauges for measuring Z-direction torque, i.e. Mz, are R9, R10, R11 and R12, wherein R9 and R10 are respectively attached to the two side surfaces of the first rectangular beam (321) along the radial central symmetry axis and close to the inner end edges, R11 and R12 are respectively attached to the two side surfaces of the third rectangular beam (323) along the radial central symmetry axis and close to the inner end edges, or R9 and R10 are respectively attached to the two side surfaces of the second rectangular beam (322) along the radial central symmetry axis and close to the inner end edges, R11 and R12 are respectively attached to the two side surfaces of the fourth rectangular beam (324) along the radial central symmetry axis and close to the inner end edges, and R9, R10, R11 and R12 form a Wheatstone full-bridge circuit III; The four rectangular beams have the same size and are located between the loading ring (31) and the force transmission column (33); the upper end surface of the loading ring (31) is higher than the upper end surface of the force transmission column (33) by at least 2 mm; the upper end surface of the force transmission column (33) is higher than the upper surface of the rectangular beams by at least 1 mm; the annular diaphragm (34) is located between the fixing ring (35) and the force transmission column (33) and at the lower end of the force transmission column (33), the lower end surface of the force transmission column (33) is higher than the lower end surface of the annular diaphragm (34) by at least 1 mm; there is a gap between the lower end surface of the four rectangular beams and the upper end surface of the annular diaphragm (34).

3. The six-dimensional force sensor according to claim 2, wherein The annular diaphragm (34) is provided with three groups of strain gauges, each group having four strain gauges, to form a second Wheatstone full-bridge circuit; the second Wheatstone full-bridge circuit is used to measure X-direction force, Y-direction force and Z-direction force. The strain gauges for measuring the X-direction force Fx are R13, R14, R15 and R16, which constitute a Wheatstone full-bridge circuit IV and are respectively adhered along the X-axis direction of the annular diaphragm (34); The strain gauges for measuring the Y-direction force Fy are R17, R18, R19 and R20, which constitute a Wheatstone full-bridge circuit V and are respectively adhered along the Y-axis direction of the annular diaphragm (34); The strain gauges for measuring the Z-direction force Fz are R21, R22, R23 and R24, which constitute a Wheatstone full-bridge circuit VI and are respectively adhered along the diameter direction of the annular diaphragm (34) which is rotated by 45° with respect to the Y-axis or the Z-axis; the strain gauges in the Fx, Fy and Fz directions are all adhered at the outer diameter and the inner diameter of the annular diaphragm (34).

4. The six-dimensional force sensor according to claim 2, wherein the circular flat plate (11) and the circular ring column (12) are integrally formed; the circular flat plate (11) is provided with a plurality of counterbores (111) and a plurality of fan-shaped holes (112) distributed along the circumference; the counterbores (111) on the protective end cover (1) are fixedly connected with the end cover fixing threaded holes (311) on the loading ring (31) through screws; the fan-shaped holes (112) are installed in cooperation with the fan-shaped bosses (312), and the fan-shaped bosses (312) are higher than or equal to the circular flat plate (11).

5. The six-dimensional force sensor according to claim 4, wherein the protective base comprises a bottom plate (41) and first and second bosses (42 and 43) sequentially arranged above the bottom plate (41); the first and second bosses (42 and 43) form a stepped surface (422); the bottom plate (41) is provided with a plurality of counterbores (411) and a recess in the middle; the side of the first boss (42) is provided with a cable outlet hole (421); the second boss (43) is provided with a plurality of threaded holes (431) and pin holes (432); the bottom plate (41), the first boss (42) and the second boss (43) are integrally formed; the counterbores (411) and the bottom cover fixing holes are fixedly connected through screws.

6. The six-dimensional force sensor according to claim 5, wherein a planar step (352) and a side step (353) are formed between the annular diaphragm (34) and the fixing ring (35); the bottom surface and the inner surface of the circular ring column (12) are gap-fitted with the planar step (352) and the side step (353) respectively; the upper end surface of the force transmission column (33) is gap-fitted with the lower end surface of the circular plate (25), and the lower end surface of the force transmission column (33) is gap-fitted with the stepped surface (422). The method comprises: S1, calibrating the membrane-beam type six-dimensional force sensor to obtain each-dimensional output voltage data set; S2, establishing a BPNN neural network model, taking the five-dimensional output voltage data of the six-dimensional force sensor as input and the fault-dimensional output voltage data as output; 7. The fault-tolerant measurement method of a six-dimensional force sensor according to any one of claims 1 to 6, characterized in that, S3, optimizing and training the BPNN neural network model by using a genetic algorithm to obtain optimal weight values and threshold values. ​ ​ ​ S4, putting data into the trained BPNN neural network model, using the trained BPNN neural network model to predict and output fault dimension signals, and performing fault-tolerant measurement.

8. The method of claim 7, wherein, The calibrated film-beam type six-dimensional force sensor acquires a set of output voltage data of each dimension, including: Adjusting the calibration platform, fixing the film-beam type sensor on the calibration platform by bolts, and installing a loading cap on the top thereof, calibrating the zero baseline of the output voltage of each direction of the six-dimensional force sensor, gradually increasing the load to the full range at the divided loading points in the positive / negative direction of each dimension of the six-dimensional force sensor, then gradually reducing the load to zero, recording the output voltage values, and dividing the obtained set of output voltage data of each dimension into two parts of a training set and a test set in a ratio of 7:3; The BPNN neural network model is established by taking the five-dimensional output voltage data of the six-dimensional force sensor as input and the output voltage data of the fault dimension as output, including: Taking any five-dimensional output voltage data as the input of the input layer of the BPNN neural network model, taking the remaining one-dimensional output voltage data as the output of the output layer of the BPNN neural network model, and including two hidden layers, setting the number of neurons of the hidden layer of the BPNN neural network model to 10 according to the empirical formula l=(n+m)^(1 / 2)+a, setting the activation function to sigmoid(), and setting the loss function suitable for regression problems according to experience, wherein n is the number of input layer neurons, m is the number of output layer neurons, and a is a constant between 1 and 10; The BPNN neural network model is optimized and trained using a genetic algorithm to obtain optimal weights and thresholds, including: All weights and thresholds are integrated into a chromosome, a plurality of different chromosomes are randomly generated, the optimal chromosome is obtained through selection, crossover, and mutation, the fitness function is used to evaluate the advantages and disadvantages of the chromosome to obtain an optimal set of weights and thresholds, the optimal weights and thresholds are substituted into the BPNN neural network model, the evolution number, population size, crossover probability, and mutation probability of the genetic algorithm are set, the iteration number, error threshold, and learning rate of the BPNN neural network model are set, all data are normalized, a five-dimensional and one-dimensional mapping relationship is fitted using the test set data, and the trained BPNN neural network model is verified using the test set; The data is put into the trained BPNN neural network model, the trained BPNN neural network model is used to predict and output fault dimension signals, and fault-tolerant measurement is performed, including: The five-dimensional voltage output signal of the six-dimensional force sensor with a fault in a certain dimension is put into the trained BPNN neural network model, the sixth-dimensional signal is predicted using the five-dimensional sensor signal, complete six-dimensional measurement data is obtained, and fault-tolerant measurement of the sensor is realized.

Images