An L-shaped three-dimensional force tactile sensor based on magnetostrictive effect

Abstract

This invention relates to an L-shaped three-dimensional force tactile sensor based on the magnetostrictive effect. The sensor includes a contact, an L-shaped iron-cobalt wire, a fixing element, a magnetic field sensing element (TMR), a permanent magnet, and a base. The base is annular with three sets of grooves evenly spaced on its upper surface. In each set, the groove closest to the center is the first groove, and the two outermost grooves are the second grooves, symmetrically located diagonally behind the first groove. The L-shaped iron-cobalt wire has a vertical short beam inserted into the first groove and a horizontal crossbeam pointing horizontally towards the center, inserted into the lower part of the fixing element. The contact is located at the upper end of the fixing element. Three magnetic field sensing elements (TMR) are attached to the inner wall of the base and are located directly below the L-shaped iron-cobalt wire. Compared to previous crossbeam structures, this invention offers advantages such as high sensitivity in all directions, the ability to measure dynamic and static forces, a large force measurement range, small size, high linearity, simple design, low cost, and large signal output.

Description

Technical fields:

[0001] This application pertains to tactile sensors, specifically relating to an L-shaped three-dimensional force tactile sensor based on magnetostriction. Background technology:

[0002] Research on multidimensional force sensors began earlier abroad, in the early 1970s, primarily for use in intelligent robot systems. Domestic research started relatively late, in the late 1980s. Major domestic institutions researching multidimensional force sensors include Harbin Institute of Technology, the Chinese Academy of Sciences, and Southeast University, while leading manufacturers include Aerospace Electronics, Goertek, and Dahua Technology. Three-dimensional force tactile sensors are mainly classified into capacitive, piezoresistive, piezoelectric, and piezomagnetic types. Piezoresistive tactile sensors, designed based on the piezoresistive effect, offer advantages such as high spatial resolution, simple structure, and high frequency response. However, in practical testing, they also suffer from poor repetition rate, hysteresis, high power consumption, and complex manufacturing processes. Piezoelectric tactile sensors are designed based on the piezoelectric effect of piezoelectric materials. When subjected to mechanical force, the piezoelectric material generates a voltage or charge change, converting the applied force into an electrical signal. However, they can only measure dynamic forces and have drawbacks such as low dynamic resolution and complex detection circuitry. A capacitor typically consists of two capacitor plates and a dielectric layer. When subjected to external force, the dielectric layer is compressed, causing a change in the distance between the two capacitor plates, and consequently, a change in the capacitance. These tactile sensors are characterized by simple structure, high sensitivity, high spatial resolution, and a large dynamic range, making them suitable for measuring three-dimensional tactile force. However, they suffer from poor anti-interference capabilities, hysteresis nonlinear response, and complex measurement circuitry. Furthermore, these types of sensors are complex to manufacture, expensive, and difficult to assemble.

[0003] The paper "Design of a Galfenol Cantilever Beam Three-Dimensional Force and Tactile Sensor for Intelligent Robotic Arms" (Hebei University of Technology, 2020) designs a cross-shaped structure based on gallium iron sheets. While this structure can measure three-dimensional forces, its measurement range is small and its volume is large, making it unsuitable for applications in confined spaces. The paper "Structural Design and Application of a Magnetostrictive Three-Dimensional Force and Tactile Sensor" (Hebei University of Technology, 2022) designs a cross-shaped cantilever beam structure using iron wire, improving the measurement range and sensitivity. However, due to its small measurement range and large volume, it still cannot meet the technical requirements. Summary of the Invention:

[0004] The purpose of this invention is to address the shortcomings of current technologies by proposing a magnetostrictive L-shaped iron-cobalt three-dimensional force tactile sensor. This sensor employs a circular base, three L-shaped iron-cobalt wires arranged at 120° intervals on top of it, and a contact in the center. The pressure detected by the sensor causes deformation of the magnetostrictive material, resulting in a change in the internal magnetic field. A TMR (tumor-modulated magnetic field) sensing element located directly below the L-shaped wires detects this change in magnetic field and converts it into a voltage signal output, establishing a force-magnetic field-voltage conversion relationship to determine the magnitude and direction of the three-dimensional force. Compared to previous cross-beam structures, this invention offers advantages such as high sensitivity in all directions, the ability to measure both dynamic and static forces, a large force measurement range, small size, high linearity, simple design, low cost, and large signal output.

[0005] To achieve the above objectives, this application provides the following solution:

[0006] An L-shaped three-dimensional force tactile sensor based on the magnetostrictive effect, the sensor includes a contact, an L-shaped iron-cobalt wire, a fixing element, a TMR, a permanent magnet and a base;

[0007] The base is circular, with three sets of grooves evenly distributed on its upper surface. In each set of grooves, the one closest to the center is the first groove, and the two on the outer side are the second grooves, symmetrically located diagonally behind the first groove.

[0008] In the L-shaped iron-cobalt wire, the short beam is vertical and inserted into the first groove, and the horizontal beam is horizontal and points towards the center of the circle and is inserted into the lower part of the fixing member; the upper end of the fixing member is provided with a contact.

[0009] The permanent magnets are inserted into the second groove, located on both sides of the L-shaped wire; there are 6 in total.

[0010] Three magnetic field detection elements (TMRs) are attached to the inner wall of the base and are located directly below the L-shaped iron-cobalt wire. The vertical distance between the crossbeam of the L-shaped iron-cobalt wire and the TMR is 1-2 mm.

[0011] The fastener is cylindrical and made of white resin. It has three mounting holes evenly distributed around its lower perimeter. The diameter of each hole is 1 mm, the same as the diameter of the iron-cobalt wire. The distance from the center of the mounting hole to the lower edge of the contact is 1.5 mm.

[0012] The fastener has a diameter of 8mm and a height of 3mm;

[0013] The contact is hemispherical, with the same diameter as the fixing member. It is made of white resin.

[0014] The contact is made of white resin;

[0015] The vertical length of the L-shaped wire is 2-4mm, and the horizontal length is 4-8mm.

[0016] The beneficial effects disclosed in this invention are as follows:

[0017] This invention designs an L-shaped three-dimensional force tactile sensing array based on magnetostriction. When an external force is applied to the contact, it causes the magnetostrictive metal material connected to the contact to deform, thereby changing the magnetic field inside the material. The magnetic field detection element senses the change in the magnetic field and outputs a voltage signal, completing the entire measurement process of force-magnetic field-voltage. Then, based on the derived relationship between three-dimensional force and voltage, the unknown force can be obtained. By detecting the magnitude and direction of the sensed force through the different output voltages of different channels, this structure achieves the purpose of detecting three-dimensional force. It boasts high sensitivity, reaching over 20 mV / N, capable of resolving very small forces. Simultaneously, this array can measure forces up to 16 N in the normal direction, expanding the force measurement range. Compared to the previous cross-shaped structure, it is smaller in size and, under the same conditions, has a larger output signal—more than twice that of the cross-shaped structure. The structure is also more stable, and the L-shaped wire can withstand greater forces compared to vertical wires. The fabrication process for this sensor array is simple and easy to assemble. Compared to other types of sensors, the manufacturing conditions are simple; it only requires placing readily available iron-cobalt wire in an oven to shape it into an L-shape. The base can be 3D printed, resulting in low cost. Replacing the Hall element with a TMR for the magnetic field detection element significantly improves the sensor's sensitivity. Attached image description:

[0018] 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 are briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a top view of the L-shaped three-dimensional force tactile sensing array structure based on magnetostriction in the embodiment;

[0020] Figure 2 This is a disassembled schematic diagram of the L-shaped three-dimensional force tactile sensing array structure based on magnetostriction in the embodiment.

[0021] Figure 3 This is a front view of the L-shaped three-dimensional force tactile sensing array structure based on magnetostriction in the embodiment.

[0022] Figure 4 This is a schematic diagram illustrating the measurement principle of the L-shaped three-dimensional force tactile sensing array structure based on magnetostriction in the embodiment.

[0023] Figure 5This is a schematic diagram of the circuit board for the L-shaped three-dimensional force tactile sensing array structure based on magnetostriction in Examples 1 and 2.

[0024] Figure 6 This is a schematic diagram of the Z-axis force output of the L-shaped three-dimensional force tactile sensing array structure based on magnetostriction in Experiment 1 of Example 1;

[0025] Figure 7 This is a force-displacement diagram along the x-axis of the L-shaped three-dimensional force-tactile sensing array structure based on magnetostriction in Experiment 2 of Example 2.

[0026] Figure 8 This is a force-displacement diagram along the y-axis of the L-shaped three-dimensional force-tactile sensing array structure based on magnetostriction in Experiment 2 of Example 2;

[0027] Figure 9 This is a force decomposition diagram of the tangential force on the horizontal plane of the L-shaped three-dimensional force tactile sensing array structure based on magnetostriction in the embodiment.

[0028] Among them, 1-contact; 2-L-shaped iron-cobalt wire; 3-fixing component; 4-TMR; 5-permanent magnet; 6-base. Detailed implementation method:

[0029] The technical solutions of this application 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without innovative effort are within the protection scope of this application.

[0030] To make the above-mentioned objectives and advantages of the present invention more readily understood, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0031] like Figure 1-3 As shown, an embodiment of the present invention provides an L-shaped three-dimensional force tactile sensing array based on magnetostriction, comprising a contact 1, an L-shaped iron-cobalt wire 2, a fixing member 3, a TMR 4, a permanent magnet 5, and a base 6.

[0032] The base 6 is annular, with three sets of grooves evenly spaced (at 120-degree angles) on its upper surface. In each set, the groove closest to the center is the first groove, and the two outermost grooves are the second grooves, symmetrically located diagonally behind the first groove. The center-to-center distance between each second groove and the first groove is 1.80 mm. The acute angle formed by the center of the first groove, the center of the base, and the center of the second groove in each set is 6.28 degrees. 0 ;

[0033] The distance from the three first grooves to the center of the base 6 is the same, which is 9.1mm; the distance from the six second grooves to the center of the base 6 is the same, which is 9.15mm.

[0034] In the L-shaped iron-cobalt wire 2, the short beam is vertical and inserted into the first groove, and the horizontal beam is horizontal and points towards the center of the circle and is inserted into the lower part of the fixing member 3; the upper end of the fixing member 3 is provided with a contact 1;

[0035] Permanent magnet 5 is inserted into the second groove, located on both sides of the L-shaped wire; a total of 6;

[0036] Three magnetic field detection elements TMR4 are attached to the inner wall of the base 6 and are located directly below the L-shaped iron-cobalt wire. The vertical distance between the crossbeam of the L-shaped iron-cobalt wire 2 and the TMR is 2mm.

[0037] The fixing component 3 is cylindrical and made of white resin. It has three mounting holes evenly distributed around its lower perimeter. The holes are 1mm in diameter and 2mm deep, with the wire inserted 1mm deep. The diameter of the wire is the same as that of the iron-cobalt wire. The distance from the center of the mounting hole to the lower edge of the contact is 1.5mm.

[0038] The diameter of the fastener 3 is 8mm and the height is 3mm;

[0039] The contact 1 is hemispherical, with the same diameter as the fixing member 3, and is made of white resin;

[0040] In this embodiment, to broaden the range of force measurements, an L-shaped iron-cobalt wire is selected as the magnetostrictive metal. The vertical and horizontal lengths of the L-shaped iron-cobalt wire are 3mm and 6mm, respectively. The first groove is 2mm deep and 1mm in diameter. The iron-cobalt composition is Fe. 30 Co 70 (Iron 30 Cobalt 70), three iron-cobalt wires correspond to through holes with an angle difference of 120 degrees. One end of the iron-cobalt wire is fixed on the sensor base, and the other end is connected to the contact through the hole. At the same time, the iron-cobalt wire is located directly above the magnetic field detection element and does not make contact.

[0041] The base 6 has an inner radius of 8mm, an outer radius of 16mm, and a thickness of 2mm.

[0042] The permanent magnet is a bias magnetic field permanent magnet made of neodymium iron boron; it provides a fixed and uniform bias magnetic field for the entire array. It is located 1.5 mm behind each iron-cobalt wire and is cylindrical with a radius and height of 1 mm.

[0043] Since the permanent magnet may deviate from its initial position during the experiment, it needs to be fixed in place with glue.

[0044] In this embodiment, the magnetic field detection element is a TMR, fixedly positioned near the curved section of the L-shaped iron-cobalt wire, directly below the L-shaped wire. The TMR is an integrated component that needs to be soldered onto the PCB board. As a magnetic field change detection element, the TMR has higher sensitivity than traditional Hall effect sensors, capable of sensing minute changes and converting these changes into voltage signals, which are then stored in a computer via a signal acquisition unit. Since the output voltage needs to be measured at three locations, three TMRs, model TMR2003, are required.

[0045] Depend on Figure 4 It can be seen that when the contactor senses an unknown three-dimensional force, it is transmitted to the connected L-shaped iron-cobalt wire. Due to the pressure, the wire deforms, causing a change in the magnetic field intensity within the material. The TMR detects this change in the magnetic field and converts it into a voltage output through internal circuitry. The unknown force is then solved using the acquired voltage and the derived force-voltage relationship, realizing the entire measurement process from force to magnetism to electricity back to force. Specifically, when a normal force is applied, the deformation and output voltage are the same because the three L-shaped iron-cobalt wires are symmetrical; when a tangential force is applied, the deformation and output voltage of the three L-shaped iron-cobalt wires are different. Based on the magnitude of the output voltage, the magnitude and direction of the three-dimensional force can be determined.

[0046] Figure 5 This is a circuit wiring diagram designed based on the TMR's structural diagram. The TMR has five terminals: power, V+, V-, ground, and unconnected. Since the three TMRs are the same model, they can share a common ground and power supply, with a power supply range of 0-7V. Terminal 1 connects to a 2V DC power supply, terminal 2 is unconnected, terminal 3 connects to the positive input of the data acquisition card, terminal 4 is grounded, and terminal 5 connects to the negative input of the data acquisition card. The other terminals are labeled identically. The TMR outputs are connected to the data acquisition card.

[0047] The working principle of the three-dimensional force-tactile sensing array of the present invention is as follows:

[0048] In this invention, forces in three directions need to be collected, so a polar coordinate system is adopted. When the contactor senses pressure of different magnitudes from different directions, the contactor will cause the three L-shaped iron-cobalt wires connected to it to deform to different degrees; this is the force sensing part.

[0049] Depending on the magnitude of the force, the three wires will deform to different degrees. Under the inverse magnetostriction effect and the bias magnetic field provided by the cylindrical permanent magnet, the magnetic field inside the iron-cobalt wire will change differently, which is the magnetic part.

[0050] The TMR located directly beneath the iron-cobalt wire detects changes in the magnetic field, and its output voltage changes accordingly. Different changes in the magnetic field result in different output voltage signals, which constitute the electrical component.

[0051] This completes the entire conversion process from force to magnetism to electricity. Next, the three voltage signals are transmitted to a computer via a data acquisition card or oscilloscope, and the magnitude of the three-dimensional force acting on the contact is calculated using the corresponding algorithm and formula.

[0052] To verify the measurement performance of the three-dimensional force tactile sensing array in this embodiment, two specific experiments will be conducted below.

[0053] Experiment 1: The actual output voltage curve of the sensor in the z-axis direction under the action of a static force in the vertical direction of 0-3N. The main purpose is to study the sensitivity and accuracy of the sensor array to the force in the vertical direction, and at the same time to determine the correction coefficient of the magnetic field detection element TMR in the sensor array decoupling algorithm.

[0054] Construction of the experimental platform: [The following text appears to be a fragment and requires further context for accurate translation.] Figure 1-3 The packaged sensor array shown is fixed on a multi-functional worktable with adjustable angle. The worktable remains horizontal, thus applying a vertical force. An initial voltage is provided to the sensor via a DC regulated power supply, and the sensor's output voltage is acquired by a data acquisition card and displayed on a computer.

[0055] Experimental Procedure and Results: The assembled sensor was fixed on the workbench. The three output ports of the sensor array were connected to the data acquisition card, which was also connected to the computer for subsequent data reading. VCC on the sensor is the power supply, and GND is ground. The array uses three TMRs, each requiring a DC regulated power supply. The VCC port is connected to a 2V DC voltage, and the ground terminals of the three TMRs can be grounded uniformly. Different forces were applied to the sensing unit using a press. While applying the force, the voltage signal and its changes were continuously recorded. The results are shown in the figure. The graph shows that the sensor exhibits good linearity and can measure static forces from 0 to 3N.

[0056] The software or protocols involved in this invention are all known technologies.

[0057] Figure 6 The graph shows the voltage output of the three L-shaped iron-cobalt wires when a normal force of 0-3N is applied. As can be seen, the output voltage increases by more than 10mV for every 0.5N increase. Since the three wires are identical except for their 120-degree angle difference, the changes in their deformation are essentially the same. This allows for precise measurement of the normal force when applied; similarly, the different deformations of the three wires when a tangential force is applied allow for measurement of the tangential force.

[0058] Experiment 2: Actual deformation curves of the sensor in the x and y axis tangential force directions under static force in the horizontal direction of 0-2N. The main purpose is to study the sensitivity and accuracy of the sensor array to forces in the horizontal direction, and at the same time determine the correction coefficient of the magnetic field detection element TMR in the sensor array decoupling algorithm.

[0059] Experimental platform setup: (The following text appears to be a fragment and requires further context for accurate translation.) Figure 1-2 The packaged sensor array shown is fixed on a multi-functional worktable with adjustable angle. The worktable remains horizontal, thus applying a vertical force. An initial voltage is provided to the sensor via a DC regulated power supply, and the sensor's output voltage is acquired by a data acquisition card and displayed on a computer.

[0060] Experimental Procedure and Results: The assembled sensor was fixed on the workbench. The three output ports of the sensor array were connected to the data acquisition card, which was also connected to the computer for subsequent data reading. VCC on the sensor is the power supply, and GND is ground. The array uses three TMRs, each requiring a DC regulated power supply. The VCC port is connected to a 2V DC voltage, and the grounding terminals of the three TMRs can be uniformly grounded. A pressure machine was used to apply different forces to the sensing unit in two directions: along the x-axis and along the y-axis, to measure the tangential force. The force ranged from 0 to 2N. The oblique force can be decomposed into normal and tangential forces. While applying the force, the voltage signal and its changes were continuously recorded. The results are shown in the figure. The graph shows that the sensor has good linearity and can measure static forces from 0 to 2N.

[0061] Figure 7 The figure shows the deformation of the three L-shaped iron-cobalt wires when a tangential force is applied along the positive half of the X-axis. As can be seen from the figure, the different deformations of the three wires result in different output voltages, which can be used to measure the tangential force along the X-axis.

[0062] Figure 8 The figure shows the deformation of the three L-shaped iron-cobalt wires when a tangential force is applied along the positive half of the Y-axis. As can be seen from the figure, the different deformations of the three wires result in different output voltages, which can be used to measure the tangential force along the Y-axis.

[0063] Figure 9 This is the decomposition of the tangential force in the horizontal plane, where the coordinate system is established with the y-axis along the direction of the wire. The tangential force causes the wire to have an up-and-down deformation effect and a left-and-right swaying effect. This decomposition is used to derive the force-voltage relationship.

[0064] The software or protocols involved in this invention are all known technologies.

[0065] The experiments described above demonstrate that this design features a simple structure, uncomplicated manufacturing process, low production cost, and high measurement accuracy and sensitivity. It can measure both dynamic and static forces, exhibiting good linearity in both vertical and horizontal directions. When mounted on a robotic arm, it enables the arm to sense three-dimensional forces, determine force direction, and recognize textures, thus providing the robotic arm with a more intelligent ability to perceive objects.

[0066] The above embodiments are merely illustrative of the design and are not intended to limit it. Those skilled in the art can make various modifications without departing from the spirit and scope of this application. Therefore, all variations, improvements, and technical solutions fall within the scope of this design, and the patent protection scope of this invention should be defined by the preceding claims.

[0067] Matters not covered in this invention are common knowledge.

Claims

1. An L-shaped three-dimensional force tactile sensor based on magnetostrictive effect, characterized in that... The sensor includes a contact, an L-shaped iron-cobalt wire, a fixture, a TMR, a permanent magnet, and a base; The base is circular, with three sets of grooves evenly distributed on its upper surface. In each set of grooves, the one closest to the center is the first groove, and the two on the outer side are the second grooves, symmetrically located diagonally behind the first groove. In the L-shaped iron-cobalt wire, the short beam is vertical and inserted into the first groove, and the horizontal beam is horizontal and points towards the center of the circle and is inserted into the lower part of the fixing member; the upper end of the fixing member is provided with a contact. The permanent magnet is inserted into the second groove, located on both sides of the L-shaped wire; Three magnetic field detection elements (TMRs) are attached to the inner wall of the base and are located directly below the L-shaped iron-cobalt wire. The fastener is cylindrical with three mounting holes evenly distributed around its lower perimeter.

2. The L-shaped three-dimensional force tactile sensor based on magnetostrictive effect as described in claim 1, characterized in that: The fastener has a diameter of 8mm and a height of 3mm.

3. The L-shaped three-dimensional force tactile sensor based on magnetostrictive effect as described in claim 1, characterized in that: The contact is hemispherical, with the same diameter as the fixing member, and is made of resin.

4. The L-shaped three-dimensional force tactile sensor based on magnetostrictive effect as described in claim 1, characterized in that the vertical length of the L-shaped wire is 2-4 mm, the horizontal length is 4-8 mm, and the vertical height of the crossbeam of the L-shaped iron-cobalt wire from the TMR is 1-2 mm.

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