Stewart structure six-dimensional force sensor and assembling method thereof

Abstract

A kind of Stewart structure six-dimensional force sensor and its assembling method, it is related to a six-dimensional force sensor and assembling method.Six measurement struts are hinged and installed between bottom plate and top plate based on Stewart parallel structure, measurement strut is connected by connecting base at both ends, connecting base is provided with bearing seat and is internally equipped with thrust aligning roller bearing, measurement strut is coaxially fixed sensor pre-tightening assembly between upper end installation flange and lower end installation flange, one-way piezoelectric sensor is pre-tightening installed in the middle position of sensor pre-tightening assembly, upper end installation flange and lower end installation flange outside end are respectively coaxially extended step shaft and corresponding thrust aligning roller bearing interference fit, step shaft is sleeved with collar and then is fastened by locking nut.Each component has strong detection capability, is easy to install, has strong bearing capacity, one-way piezoelectric sensor range is adjustable, and the installation precision of measurement strut and sensor measurement precision can be improved in assembly stage.

Description

TECHNICAL FIELD

[0001] The application relates to a six-dimensional force sensor and an assembling method, in particular to a Stewart structure six-dimensional force sensor and an assembling method thereof, and belongs to the technical field of sensor research and development. BACKGROUND

[0002] A multi-dimensional force sensor can generally detect multi-component forces / torques in a space coordinate system, wherein a six-dimensional force sensor can most comprehensively detect three orthogonal force components and three orthogonal torque components in a specified space coordinate system, and existing six-dimensional force sensors are mainly in the forms of an integrated structure and a Stewart parallel structure.

[0003] The integrated structure includes a vertical beam type, a horizontal beam type, a composite beam type, a cylindrical type, a circular cylindrical type and the like, and has the advantages of high rigidity and compact structure. However, since there is a certain degree of force coupling between the measurement sensitive parts, that is, the output signals of the strain bridges are associated with each force / torque component, the measurement signals cannot be completely decoupled, thereby affecting the measurement accuracy.

[0004] The Stewart parallel structure is a six-dimensional force sensor structure based on a Stewart platform, and has the characteristics of high rigidity, stable structure, strong bearing capacity, no error accumulation and simple inverse solution solving. The current Stewart parallel structure generally adopts a spherical hinge connection mode, and the sensitive elements are arranged on the measurement branch rods. Since there is no stress coupling between the measurement branch sensitive elements, it is not necessary to realize decoupling by changing the patch mode, and this characteristic makes the six-dimensional force sensor based on the Stewart parallel structure have high measurement accuracy.

[0005] However, the current six-dimensional force sensor based on the Stewart parallel structure still has the following problems:

[0006] 1. The detection capabilities of the components are greatly different, and there is a large nonlinear error, a return error or a repeat error in one or more directions, which limits the practical application of the sensor;

[0007] 2. The spherical hinge connection mode needs to pre-tighten twelve spherical hinges on six rods during assembly, and needs to ensure that the pre-tightening forces are consistent, so the assembly is relatively complex. If the pre-tightening force is too large, since the contact area of the spherical hinge and the spherical socket is large, the pre-tightening friction force will be too large, causing the measurement branches to have large stress coupling and being difficult to decouple, which seriously affects the measurement accuracy. At the same time, the spherical pair inevitably has a gap, resulting in a large nonlinear error and a return error of the sensor;

[0008] 3. Some six-dimensional force sensors based on Stewart parallel structure use a flexible hinge that is cut in one piece at the connection point. Although this can effectively avoid the friction and gap problems caused by ball joints, the connection point is very fragile, has poor load-bearing capacity, and there is a certain degree of force / torque coupling at the connection point.

[0009] 4. Generally, six-dimensional force sensors based on Stewart parallel structure use strain gauges or strain-type unidirectional force sensors for each measuring rod. The range is fixed and it is difficult to achieve a large range measurement. When performing a large range measurement, there is a large nonlinear error.

[0010] 5. In the assembly stage, the traditional method of measuring rod length using combined gauge blocks is quite common. However, the accuracy of gauge block length measurement is limited by the precision of the gauge blocks themselves and the markings on the scale. If multiple gauge blocks are used to achieve the required length during the measurement process, measurement errors may gradually accumulate, leading to inaccurate overall measurement results. Gauge block measurement usually relies on external references, such as rulers or scales. If the external reference itself has errors or is damaged, it may affect the accuracy of the measurement. Therefore, the method of measuring rod length using gauge blocks has poor repeatability, making it difficult to meet frequent measurement tasks and achieve high precision.

[0011] 6. Generally, the installation length (length along the rod length from the center of the upper hinge point to the center of the lower hinge point) of each measuring rod in a six-dimensional force sensor based on a Stewart parallel structure cannot be accurately measured. This is because it is difficult for typical measuring devices to pinpoint the center of a circle or sphere. In practice, the actual installation lengths of each measuring rod are inconsistent, leading not only to installation difficulties but also to individual rods bearing significant internal forces, thus affecting the sensor's lifespan. Since the actual installation length of the measuring rods affects the sensor's height parameter, inconsistent rod lengths directly impact the sensor's measurement accuracy. Summary of the Invention

[0012] To address the shortcomings of the prior art, this invention provides a Stewart-structured six-dimensional force sensor and its assembly method. It possesses strong detection capabilities across all components. The hinge utilizes a thrust self-aligning roller bearing for easy installation, exhibits low friction at the connection point, has strong load-bearing capacity, and eliminates force / torque coupling at the connection. The measuring rod employs a unidirectional piezoelectric sensor with an adjustable range. During the assembly stage, a rod length measuring device enhances the installation accuracy of the measuring rod and the sensor's measurement accuracy.

[0013] To achieve the above objectives, the present invention adopts the following technical solution:

[0014] A Stewart structure six-dimensional force sensor, comprising a bottom plate, a top plate, and six measurement struts based on a Stewart parallel structure hinged and installed between the edges of the two, the two ends of the measurement struts are connected to the corresponding positions of the bottom plate and the top plate through the connecting base, the connecting base comprises T-shaped support one and T-shaped support two fixed on the bottom surface of the bottom plate or the upper surface of the top plate through bolts, and a bearing seat rotatably installed at the top end of the two support arms, the bearing seat is assembled with a thrust aligning roller bearing and is fixed by a bearing seat cover, the measurement strut comprises an upper end mounting flange and a lower end mounting flange, and a sensor pre-tightening assembly coaxially fixed between the two, a one-way piezoelectric sensor is installed in the middle position of the sensor pre-tightening assembly by pre-tightening bolt and pre-tightening nut, the outer end of the upper end mounting flange and the lower end mounting flange is coaxially extended and provided with a stepped shaft and a corresponding thrust aligning roller bearing interference fit, and the outer end of the stepped shaft of the upper end mounting flange and the lower end mounting flange is sleeved with a collar and then fastened by a locking nut.

[0015] An assembly method of a Stewart structure six-dimensional force sensor, comprising the following steps:

[0016] The installation length of each measurement strut is determined, that is, the length of the center of the upper hinge hinge point to the center of the lower hinge hinge point in the length direction of the strut is determined, and the consistency of the actual installation length of each measurement strut is controlled, wherein the installation length of the measurement strut is measured and adjusted by a rod length measuring device;

[0017] The rod length measuring device comprises a bottom base plate, a center distance measuring tool, two V-shaped groove bases, and four positioning rings, the two V-shaped groove bases are slidably installed on the upper surface of the bottom base plate along the length direction and can be locked and positioned, two V-shaped support plates are arranged on both sides of each V-shaped groove base, the center distance measuring tool comprises a guide rod and adjustable measuring blocks and fixed measuring blocks installed at both ends of the guide rod, a laser distance measuring sensor is installed on one side of the adjustable measuring block, a laser reflector plate is installed on the same side of the fixed measuring block, and counterweights are respectively installed on the opposite sides of the adjustable measuring block and the fixed measuring block, a micrometer is inserted and fixed at the bottom of the fixed measuring block, the adjustable measuring block is slidably connected with the guide rod and can be locked and positioned, and a fine adjustment anvil is slidably connected with the bottom of the adjustable measuring block and can be locked and positioned;

[0018] The two ends of the measuring support rod are installed with bearing seats, and the four positioning rings are installed on the four shaft heads at the two ends of the bearing seats respectively, so that the assembly of the measured combination is completed, then the measured combination is placed horizontally on the two V-shaped groove bases through the four positioning rings, and after automatic centering, the two V-shaped groove bases are locked, then the adjustable measuring block and the fixed measuring block are initially corrected before the assembly of the center distance gauge, the inner side of the adjustable measuring block is placed downward on the plane, the position of the fine adjustment anvil is adjusted to be attached to the plane, the fine adjustment anvil is locked in this position, the inner side of the fixed measuring block is placed downward on the plane, the insertion depth of the dial gauge is adjusted to be just in contact with the plane, and the display value is zero, the dial gauge is fixed in this position, and the center distance gauge is installed on the two positioning rings on the same side of the measured combination after the assembly, so that the measuring surface of the fine adjustment anvil is attached to the side of one of the positioning rings, and the measuring end of the dial gauge is compressed and supported on the side of the other positioning ring, then the adjustable measuring block is locked and positioned with the guide rod, and according to the size chain principle, the installation length of the measuring support rod is obtained through the following formula:

[0019] A0=A1+A2+A3-A4-A5

[0020] Wherein, A0 is the length of the center of the two hinge hinge points of the measuring support rod, A1 is the distance between the inner side of the adjustable measuring block and the fixed measuring block, measured by the laser ranging sensor, A2 is the compressed amount of the measuring end of the dial gauge, A3 is the distance from the measuring surface of the fine adjustment anvil to the inner side of the adjustable measuring block, and A4 and A5 are the outer circle radii of the two positioning rings respectively.

[0021] Compared with the prior art, the beneficial effects of the present application are:

[0022] 1、The present application has strong detection capability in each component, and the nonlinear error, return error or repeat error in each direction is low;

[0023] 2、The present application uses a thrust self-aligning roller bearing at the hinge instead of a traditional ball hinge, the spherical rollers in the bearing are arranged obliquely, and since the raceway surface of the seat ring is spherical, the self-aligning performance is achieved, so that the shaft can be inclined to a certain extent, the freedom degree at the connection is ensured, the installation is convenient, separate pre-tightening is not required, the friction at the connection is small, the self-aligning bearing can automatically adjust the stress position and angle according to the load condition, the tightness of the contact is ensured, the gap is small, and the sensor has high linear precision and return precision;

[0024] 3、The present application uses a thrust self-aligning roller bearing, which has very large axial load capacity, can bear certain radial load while bearing axial load, and there is no force / torque coupling at the connection;

[0025] 4、The measuring strut of the present application adopts a unidirectional piezoelectric sensor, which is installed in the measuring strut in series by pre-tightening, and the range can be adjusted, so that the high sensitivity can be maintained in the whole measuring range, and the high linearity can be maintained when the large range is measured;

[0026] 5、The rod length measuring device in the assembling stage of the present application adopts the combination of the non-contact laser ranging sensor and the contact type micrometer, the laser ranging sensor measures the target with relatively long distance, the range can reach 550mm, the linear error is less than 0.05mm, the sampling frequency is as high as 5kHz, the accurate measurement can be carried out in the quasi-static working condition, the micrometer measures the target with relatively short distance, the range is 25mm, the rod length measuring device helps to avoid the gradual accumulation of measurement error, does not need external reference, the measurement has high repeatability, is easy to operate, meets the frequent measurement task, and high precision can be realized at the same time;

[0027] 6、The rod length measuring device in the assembling stage of the present application can accurately position the center of the circle, and then measure the installation length (the length of the extension rod in the length direction from the center of the upper hinge hinge point to the center of the lower hinge hinge point) of each measuring strut of the Stewart structure six-dimensional force sensor, the installation gap and the pre-tightening amount of the measuring strut are adjusted according to the measurement result, so that the actual installation length of each measuring strut tends to be consistent, the installation error of the sensor is greatly reduced, the assembling is facilitated, the internal force borne by each measuring strut is relatively uniform, the service life is prolonged, and the measurement precision is improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is the overall structure axonometric drawing of the Stewart structure six-dimensional force sensor of the present application;

[0029] Figure 2 It is the explosion drawing of the connecting base of the six-dimensional force sensor;

[0030] Figure 3 It is the explosion drawing of the measuring strut of the six-dimensional force sensor;

[0031] Figure 4 It is the sectional view of the sensor pre-tightening assembly of the six-dimensional force sensor;

[0032] Figure 5 It is the overall structure axonometric drawing of the rod length measuring device applied in the assembling method of the present application;

[0033] Figure 6 It is the explosion drawing of the center distance measuring tool of the rod length measuring device;

[0034] Figure 7 It is the explosion drawing of the V-shaped groove base of the rod length measuring device;

[0035] Figure 8is an exploded view of an adjustable measuring block of a rod length measuring device;

[0036] Figure 9 is a structural schematic diagram of a measuring strut and a rod length measuring device forming a closed size chain;

[0037] Figure 10 is a structural parameter space schematic diagram of a Stewart structure six-dimensional force sensor of the present application. DETAILED DESCRIPTION

[0038] The technical solutions in the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] Referring to Figure 1 Fig. 1 shows a Stewart structure six-dimensional force sensor, which comprises a bottom plate 1, a top plate 2 and six measuring struts 4 hingedly installed between the two based on a Stewart parallel structure. Each of the measuring struts 4 is connected to the bottom plate 1 and the top plate 2 at the corresponding positions through a connecting base 3 at both ends of the measuring strut 4.

[0040] Referring to Figure 2 Fig. 2 shows that the connecting base 3 comprises a T-shaped support 1 3-2, a bearing seat 3-3, a T-shaped support 2 3-4, a bearing seat cover 3-5 and two bearing seat end covers 3-1. The T-shaped support 1 3-2 and the T-shaped support 2 3-4 are symmetrically fixed at the corresponding positions on the lower surface of the bottom plate 1 or the upper surface of the top plate 2 through bolts. The bearing seat 3-3 is integrally provided with a shaft head at both ends and is rotatably installed between the shaft holes at the top ends of the arms of the T-shaped support 1 3-2 and the T-shaped support 2 3-4. In addition, 45° slopes are machined on the inner sides of the arms of the T-shaped support 1 3-2 and the T-shaped support 2 3-4 to limit the bearing seat 3-3 to keep a fixed angle inclination. The two bearing seat end covers 3-1 are installed on the shaft heads at both ends of the bearing seat 3-3 in the form of threaded connection for fastening. The bearing seat 3-3 is provided with a stepped groove and internally assembled with a thrust self-aligning roller bearing 5. The assembly opening position of the bearing seat 3-3 is limited and fixed by the bearing seat cover 3-5.

[0041] Referring to Figure 3As shown, the measuring strut 4 includes an upper end mounting flange 4-3, a sensor pre-tightening assembly 4-4, a lower end mounting flange 4-5, two locking nuts 4-1 and two shaft rings 4-2. The sensor pre-tightening assembly 4-4 is coaxially fixed between the upper end mounting flange 4-3 and the lower end mounting flange 4-5 with flanges arranged at both ends, the upper end mounting flange 4-3 and the lower end mounting flange 4-5 are respectively coaxially extended to set step shafts and correspondingly interference fit the thrust aligning roller bearings 5, the two shaft rings 4-2 are respectively sleeved on the step shafts of the upper end mounting flange 4-3 and the lower end mounting flange 4-5, and the two locking nuts 4-1 are respectively screwed and fastened with the threads machined on the outer ends of the step shafts of the upper end mounting flange 4-3 and the lower end mounting flange 4-5, while the two locking nuts 4-1 can be used to adjust the installation length of the measuring strut 4.

[0042] Referring to Figure 4 As shown, the sensor pre-tightening assembly 4-4 includes an upper pre-tightening flange 4-4-1, a one-way piezoelectric sensor 4-4-3, a centering bushing 4-4-4, a pre-tightening bolt 4-4-5, a pre-tightening nut 4-4-6, a lower pre-tightening flange 4-4-7 and two insulating washers 4-4-2. The upper pre-tightening flange 4-4-1 and the lower pre-tightening flange 4-4-7 are coaxially and symmetrically arranged, one end of the pre-tightening bolt 4-4-5 is connected with the upper pre-tightening flange 4-4-1 through threads, the centering bushing 4-4-4 is sleeved on the middle segment of the pre-tightening bolt 4-4-5 for realizing the radial positioning of the one-way piezoelectric sensor 4-4-3, the one-way piezoelectric sensor 4-4-3 is sleeved on the centering bushing 4-4-4, the two insulating washers 4-4-2 are respectively arranged between the one-way piezoelectric sensor 4-4-3 and the upper pre-tightening flange 4-4-1 and the lower pre-tightening flange 4-4-7 to prevent the loss of electric charge, the other end of the pre-tightening bolt 4-4-5 penetrates through the lower pre-tightening flange 4-4-7 and is screwed with the pre-tightening nut 4-4-6, and the one-way piezoelectric sensor 4-4-3 is applied with pre-tightening force by tightening the pre-tightening nut 4-4-6, and since the one-way piezoelectric sensor 4-4-3 can only collect pressure, if it is applied with pre-tightening force of half of the maximum range, the tension and pressure that it can detect are respectively half of the maximum range.

[0043] By reading the values of the one-way piezoelectric sensors 4-4-3 on the six measuring struts 4, the six-dimensional space load can be calculated, the signals of the six one-way piezoelectric sensors 4-4-3 are collected by two three-channel charge amplifiers, the three-channel charge amplifiers can burn the sensor configuration parameters (range, unit, sensitivity, etc.) into the amplifier firmware through serial signal, each three-channel charge amplifier outputs three differential analog signals to a data acquisition card, and the data acquisition card is connected with a control system through a PCI bus for subsequent processing of signals.

[0044] Referring to Figure 10The structural parameters of the Stewart structure six-dimensional force sensor include: the distribution radius R1 of the hinge joint points on the bottom plate, the distribution radius R2 of the hinge joint points on the top plate, the included angle between the two hinge joint points on the bottom plate far away from each other and the center point of the bottom plate the included angle between the two hinge joint points on the top plate far away from each other and the center point of the top plate the vertical height H of the two hinge joint points between the top plate and the bottom plate.

[0045] Therefore, the coordinates of the hinge joint points B1-B6 on the top plate in the coordinate system are as follows:

[0046]

[0047] The coordinates of the hinge joint points A1-A6 on the bottom plate in the coordinate system are as follows:

[0048]

[0049] The Jacobian matrix of the Stewart structure six-dimensional force sensor is as follows:

[0050]

[0051] According to the Jacobian matrix G, the mapping relationship between the forces on the six measuring struts of the Stewart structure six-dimensional force sensor and the actual six-dimensional external force is obtained:

[0052] F W =Gf

[0053] In the formula, F W is an external force matrix: F W =[F M] T =[F x F y F z M x M y M z ] T , F x , F y , F z respectively represent the forces in the x, y and z directions, M x , M y , M z respectively represent the moments in the x, y and z directions, and f is an axial force scalar matrix: f=[f1 f2 f3 f4 f5 f6] T , wherein f1-f6 respectively represent the sensor values of the six measuring struts.

[0054] Referring to Figures 5-9As shown, a kind of assembly method of Stewart structure six-dimensional force sensor, in the assembly process, the installation length of each measuring strut 4 is determined in advance, i.e. the length of the center of hinge hinge point on each measuring strut 4 to the lower hinge hinge point center extension bar length direction, and then the consistency of the actual installation length of each measuring strut 4 is controlled, wherein the installation length of measuring strut 4 is measured and adjusted by rod length measuring device. The rod length measuring device includes bottom base plate 6, center distance measuring tool 9, two V-shaped groove bases 7 and four positioning rings 8. The upper surface of the bottom base plate 6 is slidably installed with two V-shaped groove bases 7 along the length direction and can be locked and positioned, specifically, a positioning boss is arranged on the upper surface of the bottom base plate 6 along the length direction at the middle position, and the positioning boss is combined with the positioning hole of the V-shaped groove base 7 to lock and position the V-shaped groove base 7, so that the distance between the two V-shaped groove bases 7 can be adjusted. Figure 7 As shown, each of the V-shaped groove bases 7 includes a base 7-3 and two V-shaped support plates 7-2, the bottom of the base 7-3 is provided with a sliding groove matched with the positioning boss of the bottom base plate 6, and the two V-shaped support plates 7-2 are preliminarily positioned on both sides of the base 7-3 by positioning pins 7-1, and the two V-shaped support plates 7-2 are fastened and connected with the base 7-3 by locking bolts, and the V-shaped groove base 7 and the bottom base plate 6 are locked and positioned at the same time to adjust the distance between the two V-shaped groove bases 7. Figure 6 As shown, the center distance measuring tool 9 includes a guide rod 9-2 and adjustable measuring blocks 9-3 and fixed measuring blocks 9-7 installed on both ends of the guide rod 9-2, the guide rod 9-2 is preferably made of carbon fiber material to prevent radial deformation, the adjustable measuring blocks 9-3 are slidably connected with the guide rod 9-2 and can be locked and positioned, and the fixed measuring blocks 9-7 are fixedly connected with the guide rod 9-2. A laser distance measuring sensor 9-5 is fixedly installed on one side of the adjustable measuring block 9-3 through a mounting bracket 9-4, a laser reflector 9-1 is fixedly installed on the same side of the fixed measuring block 9-7, and counterweight blocks 9-6 are fixedly installed on the opposite sides of the adjustable measuring block 9-3 and the fixed measuring block 9-7 respectively, and a micrometer 9-8 is axially inserted into the bottom of the fixed measuring block 9-7 along the guide rod 9-2 and is fastened and fixed by locking screws. Figure 8As shown, the adjustable measuring block 9-3 includes a measuring block body 9-3-3, a fine adjustment anvil 9-3-6 and a fine adjustment knob 9-3-8, the measuring block body 9-3-3 is provided with a guide hole in the middle and is slidingly connected with the guide rod 9-2, and the top is provided with a second screw 9-3-4 for locking and positioning, the bottom of the measuring block body 9-3-3 is symmetrically provided with guide rail block one 9-3-2 and guide rail block two 9-3-5 to form a track groove arranged along the axis of the guide rod 9-2 in the middle, the fine adjustment anvil 9-3-6 is slidingly matched with the track groove and is locked and positioned by the first screw 9-3-1, the guide rail block one 9-3-2 and the guide rail block two 9-3-5 are provided with a fixed end plate 9-3-7 at the rear end, and the fine adjustment knob 9-3-8 is rotatably installed in the middle of the fixed end plate 9-3-7 and is rotatably matched with the fine adjustment anvil 9-3-6, and the relative position of the fine adjustment anvil 9-3-6 and the track groove can be adjusted by rotating the fine adjustment knob 9-3-8.

[0055] In combination Figure 5 As shown, the two ends of the measuring support rod 4 are provided with bearing seats 3-3, and the four positioning rings 8 are respectively installed on the four shaft heads at the two ends of the bearing seats 3-3, so that the assembly of the measured combination is completed. Then the measured combination is placed horizontally on the two V-shaped groove bases 7 through the four positioning rings 8, and the notches of the four V-shaped support plates 7-2 automatically center the four positioning rings 8, and the two V-shaped groove bases 7 are locked. Then the adjustable measuring block 9-3 and the fixed measuring block 9-7 are initially calibrated before the assembly of the center distance gauge 9, the inner side of the adjustable measuring block 9-3 is placed downward on the plane, the position of the fine adjustment anvil 9-3-6 is adjusted by the fine adjustment knob 9-3-8 to make it fit the plane, and the first screw 9-3-1 is tightened to lock and position the fine adjustment anvil 9-3-6 at this position; the inner side of the fixed measuring block 9-7 is placed downward on the plane, the insertion depth of the dial gauge 9-8 is adjusted to make it just contact the plane when the displayed value is zero, and the locking screw is tightened to tightly fix the dial gauge 9-8 at this position. After the assembly of the center distance gauge 9, it is installed on the two positioning rings 8 on the same side of the measured combination, so that the measuring surface of the fine adjustment anvil 9-3-6 is tightly attached to one side of one of the positioning rings 8, and the measuring end of the dial gauge 9-8 is compressed and supported on the side of the other positioning ring 8, and then the second screw 9-3-4 is tightened to lock and position the adjustable measuring block 9-3 and the guide rod 9-2, so that the adjustable measuring block 9-3 and the fixed measuring block 9-7 are axially positioned on the guide rod 9-2.

[0056] In combination Figure 9 As shown, the measuring support rod and the rod length measuring device form a closed size chain at this time, according to the size chain principle, A0 is a closed ring, that is, the measured size, A1, A2 and A3 are increased rings, and A4 and A5 are reduced rings, and A0 is obtained by the following formula:

[0057] A0=A1+A2+A3-A4-A5

[0058] Wherein, A0 is the length of the two hinge hinge point center of the measuring strut 4, A1 is the distance between the adjustable measuring block 9-3 and the inner side of the fixed measuring block 9-7, which is measured by the laser ranging sensor 9-5, A2 is the compression amount of the measuring end of the dial gauge 9-8, which is read from the display value of the dial gauge 9-8, A3 is the distance from the measuring surface of the fine adjustment anvil 9-3-6 to the inner side of the adjustable measuring block 9-3, which is given by the design size, A4 and A5 are the outer circle radii of the two positioning rings 8, which are also given by the design size.

[0059] Through actual inspection, it is found that by adjusting the installation gap or adjusting the pre-tightening amount of the measuring strut 4, the actual installation length of the six measuring struts 4 is finally measured to be 113.12mm-113.16mm, and each measuring strut 4 has high uniformity under the measurement accuracy of 0.1mm.

[0060] The maximum range of the pre-tightened one-way piezoelectric sensor 4-4-3 is ±30kN, and the range can be configured by a serial signal to an amplifier, and the range is set to ±1kN. The performance indicators of the Stewart structure six-dimensional force sensor are as follows:

[0061] The range of force in x, y, z directions is ±3000N, and the range of torque in x, y, z directions is ±2000N·m.

[0062] When the force and torque from the negative full range to the positive full range are applied in the x, y, z directions, the maximum nonlinear deviation is 20.1N, 19.2N, 10.8N, 8.6N·m, 9.4N·m, 19.1N·m, respectively, and the nonlinear error of the force or torque in the x, y, z directions is 0.67%, 0.64%, 0.36%, 0.86%, 0.94%, 1.91%, respectively.

[0063] When the force and torque from the negative full range to the positive full range are applied in the x, y, z directions three times, the maximum deviation of the output force and torque in the x, y, z directions is 24.9N, 21.9N, 12.3N, 13.6N·m, 12.5N·m, 19.7N·m, respectively, and the corresponding repeatability error is 0.83%, 0.73%, 0.41%, 1.36%, 1.25%, 1.97%, respectively.

[0064] When the force and torque from negative full scale to positive full scale and back to negative full scale are applied in x, y, z directions, the maximum deviation of the output force and torque in x, y, z directions is 6.9N, 7.8N, 3.9N, 5.7N·m, 6.5N·m, 8.4N·m, respectively, and the corresponding return errors are 0.23%, 0.26%, 0.13%, 0.57%, 0.65%, 0.84%, respectively.

[0065] It is apparent to a person skilled in the art that the present application is not limited to the details of the above-described exemplary embodiments, but can be implemented in other embodiments without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the present application being indicated by the appended claims rather than by the above description, and it is intended to embrace all changes and modifications that fall within the meaning and scope of equivalents of the claims. Any reference signs in the claims should not be construed as limiting the claims to the figures in which the reference signs are used.

[0066] Furthermore, it should be understood that although the present specification is described in terms of embodiments, not every embodiment according to the present specification need necessarily include every independent technical feature. The description herein of a particular embodiment, including the description of the best mode, is not intended to limit the scope of the present application to that particular embodiment. Persons skilled in the art will readily appreciate that other embodiments that are similarly modified, although not explicitly described herein, represent further embodiments according to the present specification. Thus, the scope of the present application is to be interpreted only by the claims that follow.

Claims

1. A six-dimensional force sensor of Stewart structure, comprising a bottom plate (1), a top plate (2) and six measuring struts (4) hinged between the two based on a Stewart parallel structure, characterized in that: The measuring strut (4) is connected to the bottom plate (1) and the top plate (2) at the corresponding positions through the connecting base (3) at both ends, the connecting base (3) includes T-shaped support one (3-2) and T-shaped support two (3-4) fixed on the bottom plate (1) lower surface or the top plate (2) upper surface at the corresponding positions through bolts, and the bearing seat (3-3) is rotatably installed at the top end of the two support arms, the bearing seat (3-3) is assembled with the thrust aligning roller bearing (5) and is fixed by the bearing seat cover (3-5), the measuring strut (4) includes the upper end mounting flange (4-3) and the lower end mounting flange (4-5) and the coaxially fixed sensor pre-tightening assembly (4-4) between them, the one-way piezoelectric sensor (4-4-3) is installed by the pre-tightening bolt (4-4-5) and the pre-tightening nut (4-4-6) at the middle position of the sensor pre-tightening assembly (4-4) to apply pre-tightening force, the outer end of the upper end mounting flange (4-3) and the lower end mounting flange (4-5) is coaxially extended to be provided with a stepped shaft and the corresponding thrust aligning roller bearing (5) interference fit, and the stepped shaft outer end of the upper end mounting flange (4-3) and the lower end mounting flange (4-5) is sleeved with the collar (4-2) and then fastened by the locking nut (4-1).

2. The Stewart structure six-dimensional force sensor according to claim 1, characterized in that: The T-shaped support one (3-2) and the T-shaped support two (3-4) arm inner side are machined with 45° slope to limit the fixed angle inclination of the bearing seat (3-3).

3. The Stewart structure six-dimensional force sensor according to claim 1, characterized in that: The bearing seat (3-3) is integrally provided with shaft heads at both ends and rotatably installed between the shaft holes at the top end of the T-shaped support one (3-2) and the T-shaped support two (3-4) arm, the shaft heads at both ends of the bearing seat (3-3) are installed in the form of threaded connection to fasten the two bearing seat end covers (3-1).

4. The Stewart structure six-dimensional force sensor according to claim 1, characterized in that: The centering bushing (4-4-4) is sleeved on the middle section of the pre-tightening bolt (4-4-5) for radial positioning of the one-way piezoelectric sensor (4-4-3), and the one-way piezoelectric sensor (4-4-3) is sleeved on the centering bushing (4-4-4).

5. The Stewart structure six-axis force sensor according to claim 1, characterized in that: Two insulating washers (4-4-2) are provided on the upper and lower sides of the one-way piezoelectric sensor (4-4-3) to prevent charge loss.

6. A method of assembling a Stewart structure six-axis force sensor, characterized by: The six-dimensional force sensor according to claim 1 has an assembly method comprising the following steps: The installation length of each measuring strut (4) is determined, that is, the length of each measuring strut (4) from the center of the upper hinge joint to the center of the lower hinge joint is determined, and the consistency of the actual installation length of each measuring strut (4) is controlled, wherein the installation length of the measuring strut (4) is measured and adjusted by a rod length measuring device. The rod length measuring device comprises a bottom base plate (6), a center distance gauge (9), two V-shaped groove bases (7) and four positioning rings (8), the upper surface of the bottom base plate (6) is slidably provided with the two V-shaped groove bases (7) in the length direction and can be locked and positioned, each V-shaped groove base (7) is provided with two V-shaped support plates (7-2) on both sides, the center distance gauge (9) comprises a guide rod (9-2) and adjustable measuring blocks (9-3) and fixed measuring blocks (9-7) installed on both ends of the guide rod (9-2), one side of the adjustable measuring block (9-3) is provided with a laser ranging sensor (9-5), the same side of the fixed measuring block (9-7) is provided with a laser reflector (9-1), and the opposite sides of the adjustable measuring block (9-3) and the fixed measuring block (9-7) are respectively provided with counterweight blocks (9-6), the bottom of the fixed measuring block (9-7) is provided with a micrometer (9-8) and is tightly fixed, the adjustable measuring block (9-3) is slidably connected with the guide rod (9-2) and can be locked and positioned, and the bottom of the adjustable measuring block (9-3) is slidably matched with a fine adjustment anvil (9-3-6) and can be locked and positioned. During measurement, the bearing seat (3-3) is installed at both ends of the measuring support rod (4), meanwhile, the four positioning rings (8) are respectively installed on the four shaft heads at both ends of the two bearing seats (3-3), so that the assembly of the measured combination is completed, then the measured combination is horizontally placed on the two V-shaped groove bases (7) through the four positioning rings (8), the two V-shaped groove bases (7) are locked after automatic centering, then the adjustable measuring block (9-3) and the fixed measuring block (9-7) are initially corrected before the center distance gauge (9) is assembled, the inner side of the adjustable measuring block (9-3) is downwardly placed on a plane, the position of the fine adjustment anvil (9-3-6) is adjusted so as to be attached to the plane, the fine adjustment anvil (9-3-6) is locked and positioned at this position, the inner side of the fixed measuring block (9-7) is downwardly placed on a plane, the insertion depth of the micrometer (9-8) is adjusted so as to just contact the plane when the displayed value is zero, the micrometer (9-8) is tightly fixed at this position, the center distance gauge (9) is assembled and installed on the two positioning rings (8) on the same side of the measured combination, the measuring surface of the fine adjustment anvil (9-3-6) is tightly attached to the side of one of the positioning rings (8), meanwhile, the measuring end of the micrometer (9-8) is compressed and supported on the side of the other positioning ring (8), then the adjustable measuring block (9-3) is locked and positioned with the guide rod (9-2), according to the principle of size chain, the installation length of the measuring support rod (4) is obtained through the following formula: A0=A1+A2+A3-A4-A5 Wherein, A0 is the length of the center of the two hinge hinge points of the measuring support rod (4), A1 is the distance between the inner sides of the adjustable measuring block (9-3) and the fixed measuring block (9-7), which is measured by the laser ranging sensor (9-5), A2 is the compressed amount of the measuring end of the micrometer (9-8), A3 is the distance between the measuring surface of the fine adjustment anvil (9-3-6) and the inner side of the adjustable measuring block (9-3), A4 and A5 are the outer circle radii of the two positioning rings (8) respectively.

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