Miniature six-dimensional force sensor, redundant output method and robot dexterous hand

Abstract

The present application relates to force sensor technical field, especially to a kind of micro six-dimensional force sensor, redundancy output method and robot dexterous hand, the sensor includes: lower support, with the accommodating cavity being disposed towards one end opening;Elastomer, open end of lower support is connected, including with lower support connection outer ring, from the inner wall of outer ring inwardly extending strain beam and the inner ring being set in outer ring and being connected with the inner end of strain beam;Upper support, the center of upper support has connecting part, connecting part is fixedly connected with inner ring;Wherein, the shape of accommodating cavity is adapted to the shape of inner ring and strain beam, strain beam is also pasted with star-shaped silicon strain gauge, with common node at center, current from common node flows into the star-shaped divergent state in wire grid area around it.The present application is little by the above-mentioned setting to the influence of wire resistance and temperature drift, and redundancy output is provided, so as to reduce error, improve accuracy and reliability.

Description

Technical Field

[0001] This invention relates to the field of force sensor technology, and in particular to a miniature six-dimensional force sensor, a redundant output method, and a robot dexterous hand. Background Technology

[0002] Currently, multidimensional force sensors are key components for achieving precise manipulation capabilities in robotic dexterity hands. These sensors typically employ a resistance strain gauge structure and utilize a Wheatstone bridge circuit for signal output. The most common bridge driving method in existing technology is constant voltage excitation. Constant voltage excitation refers to applying a stable and constant voltage source to the two input terminals of the measuring bridge. Its principle lies in the law of resistive voltage division. When the bridge is balanced, the output voltage is zero. When the sensor is subjected to force, causing a change in the resistance of the strain gauge, this balance is disrupted, resulting in a small voltage output signal proportional to the strain. By amplifying and decoupling the voltage output signal, the magnitude of the force is obtained.

[0003] However, in demanding applications such as miniature six-dimensional force sensors, the constant-voltage excitation scheme has the following significant limitations:

[0004] Susceptible to wire resistance and temperature drift: There are unavoidable connecting wires between the sensor and the external measurement circuit. These wires have resistance, which changes to some extent with changes in ambient temperature, requiring complex temperature compensation.

[0005] Challenges of miniaturization: Traditional constant-voltage excitation bridge schemes typically require a large number of wires. To achieve decoupled measurement of six-dimensional force, multiple independent strain gauges are usually arranged on the elastic body to form several full-bridge circuits. Each typical Wheatstone full-bridge requires four wires (two for excitation and two for output), and the entire sensor system requires dozens of leads. For miniaturized and highly integrated micro six-dimensional force sensors, excessive wiring not only greatly increases the difficulty and cost of wiring and packaging in a small space, but also makes excessive solder joints and leads a weak link in system reliability.

[0006] In view of the above-mentioned technical problems, there is an urgent need in the field for a new miniature six-dimensional force sensor and its signal processing scheme, which can effectively avoid the influence of wire resistance and temperature drift, and reduce the number of wires by optimizing the strain gauge structure and bridge excitation method, thereby improving the ease of fabrication, accuracy and reliability of the miniature six-dimensional force sensor. Summary of the Invention

[0007] In view of at least one of the above technical problems, the present invention provides a miniature six-dimensional force sensor, a redundant output method, and a robot dexterous hand, which improves the ease of processing and reliability of the force sensor by changing the strain gauge structure.

[0008] According to a first aspect of the present invention, a miniature six-dimensional force sensor is provided, comprising:

[0009] A lower support member having a receiving cavity that opens towards one end;

[0010] An elastomer, fitted to the open end of the lower support member, includes an outer ring connected to the lower support member, a strain beam extending inward from the inner wall of the outer ring, and an inner ring disposed inside the outer ring and connected to the inner end of the strain beam.

[0011] An upper support member has a connecting portion at its center, which is fixedly connected to the inner ring. When the connecting portion is connected to the inner ring, a gap is formed between the outer ring and the upper support member.

[0012] The shape of the receiving cavity is adapted to the shape of the inner ring and the strain beam, so that the inner ring and the strain beam can deform within the receiving cavity; a silicon strain gauge is also attached to the strain beam. The silicon strain gauge is a star-shaped silicon strain gauge with a common node at the center. The current flows from the common node to the surrounding wire grid region to form a star-shaped divergence state.

[0013] Furthermore, the silicon strain gauge is rectangular in shape, including a first wire grid region and a second wire grid region located at the two parallel sides of the rectangle, and a third wire grid region and a fourth wire grid region located between the first wire grid region and the second wire grid region. The third wire grid region and the fourth wire grid region are parallel and perpendicular to the extension direction of the first wire grid region. A common pad is provided at the common node. The common pad is connected to one end of the first wire grid region, the second wire grid region, the third wire grid region and the fourth wire grid region. A connection pad is provided on the other end from the first wire grid region to the fourth wire grid region.

[0014] Furthermore, the first wire grid region, the second wire grid region, the third wire grid region, and the fourth wire grid region each have a resistance wire that is arranged in a detour along a straight line, and a metal short-circuit portion is deposited at the inflection point of the resistance wire.

[0015] Furthermore, the star-shaped silicon strain gauge is connected to form a constant current bridge, which is configured such that a constant current source injects a constant current into the common pad of the star-shaped silicon strain gauge to drive the constant current bridge.

[0016] Furthermore, each wire grid region forms a resistor, and the bridge arms of the constant current bridge are composed of resistors on at least two star-shaped silicon strain gauges. The resistors corresponding to two parallel wire grid regions on the star-shaped silicon strain gauges and the resistors corresponding to two parallel wire grid regions on another star-shaped silicon strain gauge are respectively connected to the four bridge arms of the constant current bridge. The center pads of the two star-shaped silicon strain gauges serve as the injection points of the constant current source, thus forming the constant current bridge.

[0017] Furthermore, the resistors connected to the constant current bridge are selected from: star-shaped silicon strain gauges arranged on the surface of the strain beam facing the upper support member; and star-shaped silicon strain gauges arranged on the surface of the strain beam facing the lower support member.

[0018] Furthermore, the strain beam is connected to the surface of the inner or outer ring through a stress groove. The stress groove is perpendicular to the length of the strain beam and extends through both sides. The depth of the stress groove is 5% to 30% of the thickness of the strain beam.

[0019] Furthermore, the stress groove is a straight groove or an arc groove, and the cross-section of the stress groove is U-shaped, semi-circular, or triangular.

[0020] Furthermore, the star-shaped silicon strain gauges arranged on different patch surfaces are connected to form a constant voltage bridge. Each wire grid region forms a resistor. Four resistors from two or more of the star-shaped silicon strain gauges are connected end to end to form a closed loop. The common pads of the different star-shaped silicon strain gauges are respectively used as the positive and negative excitation terminals to form a full-bridge bridge.

[0021] According to a second aspect of the present invention, a method for redundant output of the above-mentioned miniature six-dimensional force sensor is also provided, comprising the following steps:

[0022] A constant current is injected into the common pad and then shunt through the first wire grid region, the second wire grid region, the third wire grid region and the fourth wire grid region to the outer end of each region. After passing through the measurement circuit or the resistance circuit, it returns to the negative terminal of the power supply.

[0023] The voltage signals of each wire grid region are acquired and differentially measured. The information required for force decoupling is obtained through at least 6 output differential signals.

[0024] If one of the output values ​​exceeds the set range, an error will be reported, or the signal of the out-of-range signal will be removed.

[0025] The signal from the normal channel is weighted and averaged to obtain the bridge signal, and the final force value is obtained through decoupling.

[0026] According to a third aspect of the invention, a robotic dexterous hand is also provided, comprising a miniature six-dimensional force sensor as described in any one of the first aspects.

[0027] The beneficial effects of the present invention are as follows: The present invention connects the lower support member to the outer ring of the elastic body, and the upper support member is connected to the inner ring of the elastic body through the connecting part, so that the upper support member is subjected to force and the force is transmitted to the lower support member through the strain beam. Furthermore, the star-shaped silicon strain gauges formed by the silicon strain gauges set on the strain beam can reduce the number of wires because the star-shaped silicon strain gauge pattern has common nodes, thereby improving the convenience and reliability of processing.

[0028] Furthermore, a constant current bridge circuit is preferably adopted. Compared with the traditional constant voltage excitation, it can theoretically significantly reduce the impact of wire resistance and its temperature drift on the measurement results, improving the accuracy and reliability of the output. Moreover, through redundant output design, the silicon strain gauge constitutes a constant current bridge circuit with at least two outputs. The redundant output method, including constant current injection, differential measurement, out-of-range signal rejection, and normal channel weighted averaging, reduces errors and further improves reliability. In addition, the star-shaped silicon strain gauge does not affect the realization of the traditional constant voltage excitation. The resulting bridge structure that can be used for accurate measurement is diversified, reducing the number of leads and breaking through the application range of the miniature six-dimensional force sensor, reducing the limitations of its use. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of the miniature six-dimensional force sensor in Embodiment 1 of the present invention;

[0031] Figure 2 This is a schematic diagram of the AA-direction cross-sectional structure of the miniature six-dimensional force sensor in Embodiment 1 of the present invention;

[0032] Figure 3 This is a schematic diagram of the lower support member in Embodiment 1 of the present invention;

[0033] Figure 4 This is a schematic diagram of the exploded disassembly structure of the miniature six-dimensional force sensor in Embodiment 1 of the present invention;

[0034] Figure 5 This is a schematic diagram of the silicon strain gauge in Embodiment 1 of the present invention;

[0035] Figure 6 This is a schematic diagram showing the patch positions of the elastic bodies of the three strain beams in Embodiment 1 of the present invention;

[0036] Figure 7 This is a schematic diagram showing the patch positions of the elastic bodies of the four strain beams in Embodiment 1 of the present invention;

[0037] Figure 8 This is a schematic diagram of the circuit topology of the constant current bridge in the four strain beams in Embodiment 1 of the present invention;

[0038] Figure 9 This is a schematic diagram of different cross-sectional shapes of the stress groove in Embodiment 1 of the present invention;

[0039] Figure 10 This is a schematic diagram of different connection forms between the strain beam and the inner or outer ring in Embodiment 1 of the present invention;

[0040] Figure 11 This is a schematic diagram of a wiring method for using star-shaped silicon strain gauges in three strain beams in Embodiment 2 of the present invention;

[0041] Figure 12 This is a schematic diagram of the first circuit topology of the constant voltage bridge in the four strain beams in Embodiment 2 of the present invention;

[0042] Figure 13 This is a schematic diagram of the second circuit topology of the constant voltage bridge in the four strain beams in Embodiment 2 of the present invention;

[0043] Figure 14 This is a schematic diagram of the third circuit topology of the constant voltage bridge in the four strain beams in Embodiment 2 of the present invention;

[0044] Figure 15 This is a flowchart illustrating the steps of the redundant output method for a miniature six-dimensional force sensor in Embodiment 3 of the present invention.

[0045] Reference numerals: 1. Lower support; 11. Receiving cavity; 2. Elastomer; 21. Outer ring; 22. Strain beam; 22a. Stress groove; 23. Inner ring; 3. Upper support; 31. Connecting part; 32. Receiving groove; 4. Silicon strain gauge; 41. First wire grid region; 42. Second wire grid region; 43. Third wire grid region; 44. Fourth wire grid region; 45. Common pad; 46. Interconnect pad; 47. Metal short circuit part. Detailed Implementation

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0047] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0049] Example 1

[0050] like Figures 1 to 10 The miniature six-dimensional force sensor shown includes a lower support 1, an elastic body 2, and an upper support 3. Please refer to the following for details. Figures 1 to 4 In an embodiment of the present invention, the lower support member 1 has a receiving cavity 11 with an opening at one end, which provides deformation space for the deformation of the elastic body 2. The elastic body 2 is fitted and connected to the open end of the lower support member 1, including an outer ring 21 connected to the lower support member 1, a strain beam 22 extending inward from the inner wall of the outer ring 21, and an inner ring 23 disposed inside the outer ring 21 and connected to the inner end of the strain beam 22. Specifically, in an embodiment of the present invention, the elastic body 2 is the core component of the force sensor, which needs to have excellent elastic properties, high fatigue strength, and stable mechanical properties. Generally, high-strength aluminum alloy, titanium alloy, or stainless steel materials are selected, such as 7075-T6 or stainless steel 17-4P. H, which has high specific strength and fatigue performance in miniaturized processing; in specific processing, it can be processed by machining center or wire EDM, such as using precision machinery such as precision CNC milling machine or slow wire EDM machine. Among them, 17-4PH material needs to undergo solution treatment, cold treatment and aging treatment before processing: solution treatment temperature 950~1100℃, holding temperature for 30~60 minutes; cold treatment temperature below -80℃, holding temperature for 8 hours; aging treatment temperature 350-420℃, holding temperature for more than 2 hours.

[0051] In addition, the elastomer 2 can also be formed by SLM-based metal 3D printing. The material can be metal powder with a diameter of less than 0.05 mm. Through the micron-level 3D printing process, the problem of miniaturization of the elastomer 2 is solved on the one hand, and the material properties can be improved and stress in the processing can be eliminated by improving the process.

[0052] Specifically, metal powder with a diameter of 15-45 μm and a pH of 17-4 can be selected, with an oxygen and nitrogen content of less than 0.1%. The metal powder is directly thermally acted upon by a laser, specifically a fiber laser. The printing parameters can be set as follows: wavelength 1064nm, power 100-400 W, scanning speed 600-1200 mm / s, scanning spacing 0.05–0.12 mm, layer thickness 20-40 μm, and microbeam thickness 20 μm. The scanning angle is controlled by rotating adjacent layers by 67° or 90° to reduce anisotropy during printing. During the printing process, argon or nitrogen gas is used for protection, the oxygen content must be less than 0.1%, and the substrate heating temperature is 150-200℃ to reduce the thermal gradient and decrease residual stress and warping.

[0053] After printing, the semi-finished form of elastomer 2 needs to be post-processed. The support is removed by mechanical or electrical discharge machining, and residual powder is removed by ultrasonic cleaning and compressed gas blowing. Then, hot isostatic pressing is performed, using high temperature and high pressure gas. For example, for stainless steel 17-4PH, the hot pressing temperature range is 900~980℃ and the high pressure gas pressure range is 50~150MPa. Under the action of high temperature, the plasticity of elastomer 2 is enhanced, and the porosity gradually closes and diffuses under the drive of high pressure.

[0054] The upper support member 3 has a connecting part 31 at its center. The connecting part 31 is fixedly connected to the inner ring 23. When the connecting part 31 is connected to the inner ring 23, a gap is formed between the outer ring 21 and the upper support member 3. It should be noted that, in the embodiment of the present invention, the gap between the outer ring 21 and the upper support member 3 can be a protrusion on the upper surface of the inner ring 23 or a protrusion on the connecting part 31. The gap formed by the fit allows the upper support member 3 to move downward when subjected to external force, thereby causing the strain beam 22 on the elastic body 2 to deform. The strain gauge is used to detect and decouple the force value for output.

[0055] The number of strain beams 22 is a key structural parameter for achieving multidimensional force measurement; to facilitate patching and wiring operations in confined operating spaces, the number of strain beams is generally set to three or four, with the following layout: Figure 6 and Figure 7As shown, in this embodiment of the invention, at least three strain beams 22 are provided and are evenly distributed in the circumferential direction. Of course, those skilled in the art can also provide four or more strain beams 22 as needed to further improve the accuracy of force measurement. The evenly distributed circumferential layout of the strain beams 22, combined with the silicon strain gauges 4 attached to the front and back surfaces of the strain beams, provides sufficient independent measurement information for six-dimensional force decoupling. It should be noted that in this embodiment of the invention, a threaded hole for connection to the lower support body is provided on the outer ring 21 of the elastic body 2, and a threaded hole for connection to the upper support body is provided on the inner ring 23 of the elastic body 2. The connection between the three is achieved by providing countersunk holes on the upper and lower support bodies respectively.

[0056] The following explanation illustrates the principle of attaching silicon strain gauges to eight mounting areas on the front and / or back surfaces of the four strain beams: To measure six force / torque components (Fx, Fy, Fz, Mx, My, Mz), at least six independent strain measurement channels sensitive to different components are required. Therefore, at least six sets of independent output bridge circuits need to be constructed. When the upper support 3 is subjected to force, the force is transmitted to the strain beam 22 through the inner ring 23. Due to the annular uniformly distributed structure of the strain beams, radial forces (such as Fx, Fy), axial forces (Fz), and moments (Mx, My, Mz) will produce different and distinguishable stress / strain distributions on each strain beam. Since the solution of the matrix needs to ensure stability, the actual number of strain information collected should be greater than or equal to the dimension of the force to be measured, that is, the number of measurement points should be greater than or equal to six dimensions, and the non-singularity of the matrix should be guaranteed. By attaching star-shaped silicon strain gauges on the front and / or back surfaces (4×2 patch areas) of each strain beam, and setting four independent wire grid areas on each strain gauge, at least six independent strain signals can theoretically be physically obtained. Using these redundant independent strain signals, a sensitivity matrix between strain change and six-dimensional force can be established according to finite element analysis and experimental calibration, thereby achieving the above requirements. Moreover, the four uniformly distributed strain beams provide a stable and symmetrical stress distribution, which greatly supports the stable solution of the six-dimensional force decoupling algorithm, thus obtaining six sets of force values ​​with high accuracy.

[0057] like Figure 3As shown in the embodiment of the present invention, the shape of the receiving cavity 11 is adapted to the shape of the inner ring 23 and the strain beam 22, so that the inner ring 23 and the strain beam 22 can deform within the receiving cavity 11. That is, the receiving cavity forms a corresponding assembly relationship with the inner ring and the strain beam, which can ensure the positioning and limiting function of the receiving cavity on the inner ring, and at the same time avoid interference with the strain beam, so as to ensure the accuracy of the stress change sensing detection results. A silicon strain gauge 4 is also attached to the strain beam 22. The silicon strain gauge 4 is a star-shaped silicon strain gauge with a common node at the center. The current flows from the common node to the surrounding wire grid area to form a star-shaped divergence state. That is, the common node at the center serves as a common connection point for the surrounding wire grid area. When wiring to build a circuit, an equal amount of current can be input to the surrounding wire grid area by wiring at the common node.

[0058] In the embodiments of the present invention, the silicon strain gauge 4 itself is brittle. When the traditional bonding process uses adhesive to attach the silicon strain gauge 4 to the elastomer 2, it is easy to break during bonding and pressure application, or the uneven thickness of the adhesive layer during bonding will also affect the zero point and sensitivity of the sensor. In order to improve the reliability of the bonding of the silicon strain gauge 4, a fusion welding method is adopted for bonding, that is, the glass powder is melted by heating, so that the silicon strain gauge 4 is uniformly attached to the strain beam 22. The structure corresponding to this bonding will be described in detail in the following parts of the present invention. It should be noted that during the bonding process, firstly, adhesive (glass glue) is applied to one side of the elastomer 2, followed by heat curing at a temperature range of 520-560℃. Then, adhesive is applied to the opposite side of the elastomer 2, and heat curing is performed again at a temperature range of 520-560℃. After completing double-sided adhesive application, the silicon strain gauge 4 is then attached to one of the adhesive-applied surfaces and heat-cured again at a temperature range of 450-520℃. Next, the silicon strain gauge 4 is attached to the opposite adhesive-applied surface, and similarly heat-cured again at a temperature range of 450-520℃. By adopting a process sequence of first applying adhesive to all surfaces and then attaching the strain gauges sequentially, and by controlling the post-application heat curing temperature to be higher than the heat curing temperature when attaching the silicon strain gauge 4, good adhesion between the silicon strain gauge 4 and the elastomer can be ensured while avoiding thermal damage to the silicon strain gauge 4 and problems such as weak adhesion.

[0059] In the above embodiment, the lower support member 1 is connected to the outer ring 21 of the elastic body 2, and the upper support member 3 is connected to the inner ring 23 of the elastic body 2 via the connecting part 31, so that when the upper support member 3 is subjected to force, it is transmitted to the lower support member 1 through the strain beam 22. By using star-shaped silicon strain gauges with common nodes on the strain beam 22, the number of wires can be reduced, thereby improving the convenience and reliability of processing.

[0060] Furthermore, a constant current bridge circuit is preferably adopted. Compared with the traditional constant voltage excitation, it can theoretically significantly reduce the influence of wire resistance and its temperature drift on the measurement results, thereby improving the accuracy and reliability of the output. Moreover, through redundant output design, the silicon strain gauge 4 constitutes a constant current bridge circuit with at least two outputs. The redundant output method, including constant current injection, differential measurement, out-of-range signal rejection, and normal channel weighted averaging, reduces errors and further improves reliability. In addition, the star-shaped silicon strain gauge does not affect the realization of the traditional constant voltage excitation. The resulting bridge structure that can be used for accurate measurement is diversified, breaking through the application range of the miniature six-dimensional force sensor and reducing the limitations of its use.

[0061] Based on the above embodiments, such as Figure 4 As shown, in some embodiments of the present invention, the connecting portion 31 protrudes from the lower surface of the upper support member 3, and the connecting portion 31 has a receiving groove around its periphery that is adapted to the strain beam 22. By providing a receiving groove around the connecting portion 31, the elastic member can deform not only toward the lower support member 1 but also toward the upper support member 3, thereby improving the accuracy of force measurement.

[0062] Please continue to refer to Figure 4 In an embodiment of the present invention, the surface of the strain beam 22 facing the upper support 3 is the front-mounted surface, and the surface of the strain beam 22 facing the lower support 1 is the back-mounted surface. The silicon strain gauge 4 is attached to the front-mounted surface and / or the back-mounted surface. That is, in an embodiment of the present invention, the silicon strain gauge 4 can be attached to the front or the back of the strain beam 22. Furthermore, it should be noted that when attaching the silicon strain gauge 4, the specific attachment position can be near the inner ring 23 or near the outer ring 21 of the strain beam 22, and those skilled in the art can choose according to actual needs.

[0063] In the embodiments of the present invention, the silicon strain gauge 4 employs MEMS (Micro-Electro-Mechanical Systems) technology, a micrometer-level fabrication technique that simultaneously manufactures an integrated system of micro-mechanical structures and micro-electronic circuits on materials such as silicon wafers. The specific fabrication method involves forming a resistor, i.e., a wire grid region, through ion implantation; the specific structural form is as follows... Figure 5As shown, the silicon strain gauge 4 is rectangular in shape, including a first wire grid region 41 and a second wire grid region 42 located at the two parallel sides of the rectangle, and a third wire grid region 43 and a fourth wire grid region 44 located between the first wire grid region 41 and the second wire grid region 42. The third wire grid region 43 and the fourth wire grid region 44 are parallel and perpendicular to the extension direction of the first wire grid region 41. A common pad 45 is provided at the common node. The common pad 45 is connected to one end of the first wire grid region 41, the second wire grid region 42, the third wire grid region 43 and the fourth wire grid region 44. A connecting pad 46 is provided on the other end of the first wire grid region 41 to the fourth wire grid region 44. The first wire grid region 41 and the second wire grid region 42 are vertically arranged and are both used to sense the force of the strain beam 22 in the same direction. The third wire grid region 43 and the fourth wire grid region 44 are horizontally arranged and are both used to sense the deformation of the strain beam 22 in another vertical direction. With this structural form, on the one hand, the number of strain gauges is reduced, so that the same strain gauge can sense the deformation in at least two directions. On the other hand, the two wire grid regions in each direction also provide a basis for subsequent redundant output.

[0064] In an embodiment of the present invention, star-shaped silicon strain gauges are connected to form a constant current bridge. The constant current bridge is configured such that a constant current source injects a constant current into the common pad of the star-shaped silicon strain gauges to drive the constant current bridge. The currents of the two differential circuits in each output circuit of the constant current bridge are equal. Each wire grid region forms a resistor. The bridge arms of the constant current bridge are formed by resistors from at least two star-shaped silicon strain gauges. Resistors corresponding to two parallel wire grid regions on one star-shaped silicon strain gauge and resistors corresponding to two parallel wire grid regions on another star-shaped silicon strain gauge are selected and connected to the four bridge arms of the constant current bridge. The center pads of the two star-shaped silicon strain gauges serve as the injection points of the constant current source, thus forming the constant current bridge. When using constant voltage excitation, there is always a wire between the sensor and the measurement circuit. This wire has resistance, which changes with ambient temperature. Since a constant voltage source is applied to the bridge, this resistance change causes variations in the measured results. Specifically, under constant voltage, changes in wire resistance cause voltage fluctuations at the bridge output. By using a constant current source for excitation, a constant current excitation is achieved. This ensures that the current injected into the bridge remains absolutely constant regardless of the wire resistance. Consequently, the wire resistance only causes changes in the voltage across the constant current source, while the current flowing through the bridge remains constant. The bridge output depends only on this current and the resistance of the bridge arms. Therefore, the influence of resistance is perfectly avoided, meaning the current in the two branches of each differential circuit in the constant current bridge is equal. Constant current excitation significantly reduces the impact of wire resistance and its temperature on the measurement results.

[0065] The resistors connected to the constant current bridge are selected from: star-shaped silicon strain gauges arranged on the surface of the strain beam facing the upper support member; and star-shaped silicon strain gauges arranged on the surface of the strain beam facing the lower support member, i.e., resistors selected from star-shaped strain gauges attached to both sides of the front and back surfaces.

[0066] Specifically, such as Figures 7 to 8 As shown, a schematic diagram of the patch configuration and circuit topology of four strain beams 22 is provided. Star-shaped silicon strain gauges are arranged symmetrically on the first two patch surfaces 13a, and their wiring configuration can be as shown in Figure 8. For ease of explanation, it is assumed that the resistances formed by the two first wire grid regions 41 and the second wire grid region 42 on the first star-shaped silicon strain gauge are represented by R11, R12, R13, and R14, and the order is: R11 is perpendicular to R12, R12 is perpendicular to R13, and R14 is perpendicular to R12. R13 and R14 are perpendicular, and R14 and R11 are perpendicular, arranged in the order of R11-R12-R13-R14, and they share a common node; similarly, the second is represented by R21, R22, R23, R24, the third by R31, R32, R33, R34, and the fourth by R41, R42, R43, R44. On the other side of the surface, the fifth star-shaped silicon strain gauge corresponds to the first star-shaped silicon strain gauge, forming a resistor in sequence. , , , The rest follow the same pattern, including... , , , , , , , , , , , .

[0067] When wiring, select R31 and R33 on the third star-shaped silicon strain gauge and the fifth star-shaped silicon strain gauge on the other side. and Each component is connected to its respective bridge arm a~d, with the center pad serving as the injection point for the constant current source, located at R31 and R33. and A constant current Is is passed through the common point and flows to each of the terminals a, b, c, d, etc., forming a voltage U. ac and U bd U ac =Is× - Is×R31;U bd = Is× - Is×R33, the resulting voltage U ac and U bd The output signal is output 1, which achieves redundant output. Similarly, eight star-shaped silicon strain gauges can form outputs 1 to 8 (only 6 are shown in the figure), thereby meeting the requirements of six-dimensional force measurement and ensuring the decoupling effect of the bridge.

[0068] The table below shows a comparison of zero-point drift tests between the constant current excitation prototype and the traditional constant voltage excitation test prototype. The test conditions were a room temperature closed environment, a sampling period of 10 seconds, and a test duration of 1 hour. It can be seen that the constant current output has better stability and reduces the adverse effects of interference factors such as changes in wire resistance.

[0069] Table 1. Comparison of zero-point drift tests between constant current excitation and traditional constant voltage excitation test prototypes in this application.

[0070]

[0071] In embodiments of the present invention, to further improve the accuracy of force measurement, please continue to refer to... Figure 5 The first wire grid region 41, the second wire grid region 42, the third wire grid region 43, and the fourth wire grid region 44 all have resistance wires arranged in a straight line, and a metal short-circuit portion 47 is deposited at the inflection point of the resistance wire. Here, the inflection point refers to the portion other than the parallel resistance wire, such as... Figure 5 As shown, the connection points of the top and bottom two resistance wires in the first grid region 41 and the second grid region 42 are covered by metal deposition. In this embodiment of the invention, aluminum deposition is used. This method short-circuit the resistance in other directions, avoiding influence from other directions during measurement. The first grid region 41 and the second grid region 42 only experience force in a single direction, thereby further improving the detection accuracy. In this embodiment of the invention, the metal short-circuit portion 47 is at least twice the width along the length of the resistance wire. Another advantage of this design is that it ensures a strong bond of the resistance wire portion during the bonding process of the silicon strain gauge 4, when the glass is fused to bond the silicon strain gauge. In the silicon strain gauge 4, the resistance wire is fabricated along a specific crystal orientation, and silicon has a high piezoresistive coefficient. It is a tensor that depends on the crystal orientation. Therefore, for the first and second wire grid regions that are perpendicular to each other, their longitudinal piezoresistive coefficient π L and transverse piezoresistive coefficient π TThe anisotropy will vary, resulting in different resistance changes due to strain in different directions. The design of the short-circuit section 47 in this pattern can mitigate the negative effects of anisotropy to some extent. Specifically, the star-shaped silicon strain gauge 4 can be configured with a size of 1cm × 1cm, a wire width of 20~40 μm in the wire grid region, and a resistance value range of 2000~5000 Ω. The specific value can be selected according to actual needs, and no specific limit is set here.

[0072] In embodiments of the present invention, such as Figure 9 As shown in the figure, the strain beam 22 can be configured as shown in (a) to be directly connected to the inner or outer ring, or as shown in (b) and (c) to have a stress groove 22a on the surface near the inner ring 23 or the outer ring 21. The stress groove 22a is perpendicular to the length direction of the strain beam 22 and extends through both sides. The depth of the stress groove 22a is 5% to 30% of the thickness of the strain beam 22. In some embodiments of the present invention, the stress groove 22a is a straight groove or an arc groove. By setting the stress groove 22a, on the one hand, the installation stress can be isolated, and on the other hand, the geometric parameters of the groove can be used as variables to adjust the sensitivity and cross-coupling of the multidimensional force sensor in different directions.

[0073] Specifically, such as Figure 10 As shown, the stress groove 22a has a U-shaped, semi-circular, or triangular cross-section. By adjusting the cross-section, depth, width, direction, and length of the stress groove 22a, it can be used as a design variable to adjust the sensitivity of the multi-dimensional force sensor in different directions, thereby obtaining more accurate force sensing data. Furthermore, in embodiments of the present invention, the stress groove 22a can also be directly processed during the fabrication of the elastomer 2 using the aforementioned metal 3D printing method.

[0074] Example 2

[0075] This embodiment provides a star-shaped silicon strain gauge with constant voltage excitation and corresponding circuit layout. Other structures, such as the elastic body, upper support, and lower support, are set in the same way as in the first embodiment, and will not be described in detail here.

[0076] Based on the above embodiments, star-shaped silicon strain gauges arranged on different patch surfaces are connected to form a constant voltage bridge. The voltages of the two differential circuits in each output circuit of the constant voltage bridge are equal. Specifically, since the silicon strain gauge selected in this invention is a star-shaped silicon strain gauge, compared with the traditional full-bridge strain gauge, it has a central common pad structure, which forms a multi-terminal network after bridging. Its resistor arms form a common point through the common pad. Through the coupling of the common point, when a force or torque is applied in any direction, the resistance values ​​of multiple resistor arms will change simultaneously. This will cause the measured bridge output signal to be mixed with force information of multiple dimensions. The traditional constant voltage Wheatstone bridge requires four independent resistor arms to form two voltage divider branches. The output signal of each bridge is only sensitive to a specific force or torque component, while being insensitive to other components. That is, applying the traditional constant voltage bridge topology to the star-shaped silicon strain gauge will ultimately lead to instability in the process of solving the sensitivity matrix from the bridge output voltage to the six-dimensional force, making it difficult to guarantee the decoupling effect of the measured bridge signal, resulting in a sharp decrease in the accuracy of the sensor. Figures 11 to 14 As shown in the figure, this embodiment provides schematic diagrams of various circuit topologies for a constant voltage bridge in four strain beams, which can overcome the above-mentioned problems and ensure the decoupling effect of the bridge signal when the star-shaped strain gauges are used to form a constant voltage bridge. Specifically, the patch form of the constant voltage bridge can be as shown in the attached figure in Embodiment 1. Figure 7 As shown, the only difference lies in the wiring configuration. In the embodiments of this invention, the stress distribution at the strain gauge patch location is clarified through finite element analysis, and the wiring configuration of the strain gauge is rationally selected. Then, through sensor calibration testing, the strain gauge senses the change in resistance caused by the stress change at the patch location. A sensitivity matrix between the strain gauge resistance change and the six-dimensional force is established, which enables constant voltage excitation under a star-shaped silicon strain gauge and ensures the accuracy of the bridge decoupling output, thus guaranteeing sensor precision. The expression for the sensitivity matrix is ​​as follows:

[0077]

[0078] It should be noted that the bridge decoupling method using the above sensitivity matrix is ​​also applicable to the constant current bridge shown in Example 1, to ensure the accuracy of the bridge decoupling output. In addition, the different wire grid regions of the star-shaped silicon strain gauge are designed according to the force sensor's force conditions to ensure that the bridge circuit can respond to specific loading forces. By decoupling the outputs of the six bridges, the magnitudes of the six force values ​​can be obtained: forces Fx, Fy; Fz, and torques Mx, My, Mz.

[0079] The following will provide exemplary descriptions of various circuit topologies of the constant voltage bridge in this embodiment. Furthermore, as... Figure 11The diagram illustrates a wiring method for using star-shaped silicon strain gauges in three strain beams. The mounting method and the resulting resistor structure can be referenced. Figure 6 As shown, R11 and R13 on the first star-shaped silicon strain gauge and the fifth star-shaped silicon strain gauge on the other side are selected. and Each of the six star-shaped silicon strain gauges is connected to its respective bridge arm. The common node of the first star-shaped silicon strain gauge is connected to the positive terminal of the power supply, and the common node of the fifth star-shaped silicon strain gauge on the other side is connected to the negative terminal of the power supply to obtain output 1. The others are connected in the same way. The six star-shaped silicon strain gauges attached to the three strain beams can form outputs 1 to 6, which can meet the basic requirements of six-dimensional force measurement and ensure the decoupling effect of the bridge.

[0080] like Figures 12 to 14 As shown, when wiring, the following method can be used: Figure 12 The wiring configuration shown selects R31 and R33 on the third star-shaped silicon strain gauge and the fifth star-shaped silicon strain gauge on the other side. and Each component is connected to its respective bridge arm. The center pads of the two star-shaped silicon strain gauges form a common node and are connected to the positive and negative terminals of the power supply, respectively, to obtain output 1. Similarly, the second output bridge selects R41 and R43 on the fourth star-shaped silicon strain gauge and the sixth star-shaped silicon strain gauge on the other side. and Each of the eight star-shaped silicon strain gauges is connected to its respective bridge arm to obtain output 2, and so on. The eight star-shaped silicon strain gauges can form outputs 1 to 8, thereby meeting the requirements of six-dimensional force measurement and ensuring the decoupling effect of the bridge.

[0081] Based on this, it is also possible to... Figure 13 The wiring method shown involves connecting the center pad of a star-shaped silicon strain gauge fixed on one side to the positive terminal, and connecting the center pad of a star-shaped silicon strain gauge on the other side to the negative terminal. This ensures neat wiring without affecting the decoupling accuracy of each bridge output.

[0082] also, Figure 12 and Figure 13 The wiring configuration for outputs 3 to 6 can also be replaced as follows: Figure 14 The method shown involves selecting star-shaped silicon strain gauges R11, R14, R21, and R24 from adjacent strain beams on one side to form an output bridge. Other bridge configurations can be formed by selecting star-shaped silicon strain gauges from different sides of the same strain beam. Similarly, output 4 can also be selected from R14 and R34 on the front of the first strain beam and R24 on the other side. , This forms the output bridge; the other output configurations can be found in the appendix. Figure 14 Choose from the provided options.

[0083] It should be noted that the above only lists some constant voltage bridge wiring configurations. The key points of the wiring are to select the common node of the star-shaped silicon strain gauge on one side as the positive or negative terminal of the power supply. When the elastic body is under stress, the four selected resistors form an output bridge circuit, and at least one of them should have a tensile stress or compressive stress significantly higher than any of the others. It is also necessary to ensure that each resistor can only be connected to one output bridge circuit. Based on the above method, there are many variable bridge configurations, which are not listed here. As long as the above method is met, it is acceptable.

[0084] Example 3

[0085] like Figure 15 As shown in the embodiments of the present invention, a redundant output method for the above-mentioned miniature six-dimensional force sensor is also provided. The redundant output method is described in the form of a star-shaped strain gauge arranged in a constant current bridge, and includes the following steps:

[0086] S10: The constant current source is injected into the common pad 45 at the common node, and then the current is diverted through the first wire grid region 41, the second wire grid region 42, the third wire grid region 43 and the fourth wire grid region 44 to the outer end of each region, and then returns to the negative terminal of the power supply after passing through the measurement circuit or the resistance circuit.

[0087] S20: Acquire the voltage signal of each wire grid region and perform differential measurement. Obtain the information required for force decoupling through at least 6 output differential signals.

[0088] S30: When one of the output values ​​exceeds the set range, an error is reported or the signal of the out-of-range signal is rejected. It should be noted that the set range refers to a signal that is exceptionally large or shows no change compared to normal values, such as a deviation exceeding 50% of the calibration value or a change rate less than 0.01%. Alternatively, it can be compared with historical calibration data. The system stores factory calibration data; if the output data during use is found to exceed a certain proportion of the initial state, it is considered abnormal. Figure 8 As shown in the figure, taking output one as an example, after the constant current is injected at the star point, it flows through paths ac and bd respectively, forming voltages Uac and Ubd, which are the output signals of output one, thus achieving redundant output.

[0089] S40: The signal from the normal channel is weighted and averaged to obtain the bridge signal, and the final force value is obtained through decoupling; the formula for weighted averaging can be expressed as: ,in, This indicates the processed bridge signal. Indicates the weighting coefficient. This represents the bridge signal before processing; its weighting coefficients can be dynamically adjusted through real-time monitoring combined with a hierarchical update strategy to ensure the accuracy of the obtained bridge signal.

[0090] In an embodiment of the present invention, a robotic dexterous hand is also provided, including the aforementioned miniature six-dimensional force sensor. The miniature six-dimensional force sensor enables the robot to perceive the magnitude, direction, and point of application of contact forces, thereby achieving fine-grained manipulation capabilities similar to those of humans.

[0091] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A miniature six-dimensional force sensor, characterized in that, include: A lower support member having a receiving cavity that opens towards one end; An elastomer, fitted to the open end of the lower support member, includes an outer ring connected to the lower support member, a strain beam extending inward from the inner wall of the outer ring, and an inner ring disposed inside the outer ring and connected to the inner end of the strain beam. An upper support member has a connecting portion at its center, which is fixedly connected to the inner ring. When the connecting portion is connected to the inner ring, a gap is formed between the outer ring and the upper support member. The shape of the receiving cavity is adapted to the shape of the inner ring and the strain beam, so that the inner ring and the strain beam can deform within the receiving cavity; a silicon strain gauge is also attached to the strain beam. The silicon strain gauge is a star-shaped silicon strain gauge with a common node at the center. The current flows from the common node to the surrounding wire grid region to form a star-shaped divergence state. The silicon strain gauge is rectangular in shape and includes a first wire grid region and a second wire grid region located at the two parallel sides of the rectangle, as well as a third wire grid region and a fourth wire grid region located between the first and second wire grid regions. The third and fourth wire grid regions are parallel and perpendicular to the extension direction of the first wire grid region. A common pad is provided at the common node. The common pad is connected to one end of the first, second, third, and fourth wire grid regions. A connection pad is provided at the other end from the first to the fourth wire grid region. The star-shaped silicon strain gauges are connected to form a constant current bridge. The constant current bridge is configured such that a constant current source injects a constant current into the common pad of the star-shaped silicon strain gauges to drive the constant current bridge. Each wire grid region forms a resistor. The bridge arms of the constant current bridge are composed of resistors from at least two star-shaped silicon strain gauges. The resistors corresponding to two parallel wire grid regions on the star-shaped silicon strain gauges and the resistors corresponding to two parallel wire grid regions on another star-shaped silicon strain gauge are respectively connected to the four bridge arms of the constant current bridge. The center pads of the two star-shaped silicon strain gauges serve as the injection points of the constant current source, thus forming the constant current bridge. The star-shaped silicon strain gauges arranged on different patch surfaces are connected to form a constant voltage bridge. Each wire grid region forms a resistor. Four resistors from two or more star-shaped silicon strain gauges are connected end to end to form a closed loop. The common pads of different star-shaped silicon strain gauges are used as the positive and negative excitation terminals, respectively, forming a full-bridge bridge.

2. The miniature six-dimensional force sensor according to claim 1, characterized in that, The first wire grid region, the second wire grid region, the third wire grid region and the fourth wire grid region each have a resistance wire that is arranged in a detour along a straight line, and a metal short circuit portion is deposited at the inflection point of the resistance wire.

3. The miniature six-dimensional force sensor according to claim 1, characterized in that, The resistors connected to the constant current bridge are selected from: star-shaped silicon strain gauges arranged on the surface of the strain beam facing the upper support; And, star-shaped silicon strain gauges arranged on the surface of the strain beam facing the lower support.

4. The miniature six-dimensional force sensor according to claim 1, characterized in that, The strain beam is connected to the surface of the inner or outer ring via a stress groove. The stress groove is perpendicular to the length of the strain beam and extends through both sides. The depth of the stress groove is 5% to 30% of the thickness of the strain beam.

5. The miniature six-dimensional force sensor according to claim 4, characterized in that, The stress groove is a straight groove or an arc groove, and the cross-section of the stress groove is U-shaped, semi-circular, or triangular.

6. A method for redundant output of a miniature six-dimensional force sensor, applied in the miniature six-dimensional force sensor as described in any one of claims 1 to 5, characterized in that, Includes the following steps: A constant current is injected into the pad at the common node, and then shunt through the first wire grid region, the second wire grid region, the third wire grid region and the fourth wire grid region to the outer end of each region, and then returns to the negative terminal of the power supply after passing through the measurement circuit or the resistance circuit. The voltage signals of each wire grid region are acquired and differentially measured. The information required for force decoupling is obtained through at least 6 output differential signals. If one of the output values ​​exceeds the set range, an error will be reported, or the signal of the out-of-range signal will be removed. The signal from the normal channel is weighted and averaged to obtain the bridge signal, and the final force value is obtained through decoupling.

7. A robotic dexterous hand, characterized in that, Including the miniature six-dimensional force sensor as described in any one of claims 1 to 5.

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