Humanoid robot fingertip multi-dimensional force sensing device and packaging method thereof

Abstract

The application discloses a kind of humanoid robot fingertip multidimensional force sensing device and its packaging method, wafer bonding integration is carried out to MEMS three-dimensional force sensing chip and glass substrate, array of metal under bump is prefabricated at the bottom of substrate, sensing unit is small in volume, thin in thickness, high in integration, overall structure is compact and neat, can be adapted to the installation and layout space of narrow and small limited humanoid robot fingertip.In the inside of groove of upper layer flexible substrate, coaxial arrangement alignment assembly through hole is arranged, and reliable mechanical interlocking limiting structure is formed by inserting metal under bump and through hole;Meanwhile, conductive composite material is filled into through hole by dispensing process and constant temperature curing, which realizes low impedance reliable electrical interconnection between sensing electrode and lower layer circuit, and also greatly improves the locking strength of overall assembly structure, which is not easy to loosen and delaminate under long-term dynamic stress condition, and the structural reliability is excellent.

Description

Technical Field

[0001] This invention belongs to the field of sensing device technology, specifically relating to a multi-dimensional force sensing device for the fingertips of a humanoid robot and its packaging method. Background Technology

[0002] Currently, humanoid robot technology is undergoing rapid iteration and upgrading. Its application scenarios have gradually expanded from traditional industrial inspection and special operations to diversified and sophisticated fields such as home services, medical assistance, and precision electronic assembly, becoming one of the core development directions in intelligent manufacturing and public services. Interaction accuracy, compliance, and anthropomorphism are key indicators for measuring the performance of humanoid robots. As the core end effector that directly contacts the outside world and performs operations, the fingertip's force perception capability directly determines the effectiveness of the robot's precise grasping, contact feedback, and posture adjustment. It is the core support for improving the robot's interactive safety and operational flexibility. Therefore, the development of fingertip sensing systems has become a key direction for breakthroughs in humanoid robot technology. Force sensing technology is the core of fingertip sensing systems. Among them, MEMS (Micro-Electro-Mechanical Systems) force sensors have gradually replaced traditional force sensors and become the mainstream device for fingertip sensing in humanoid robots due to their outstanding advantages such as small size, light weight, fast response speed, high measurement accuracy, and low power consumption. One-dimensional force sensors use flexible pressure sensors, while MEMS three-dimensional force sensors, with their integrated structural advantages, can further improve space utilization and detection accuracy, becoming the core breakthrough point for achieving high-precision fingertip sensing. Flexible substrates, due to their good flexibility, bendability, and surface fit, can adapt to the curved surface structure and flexible deformation requirements of humanoid robot fingertips, providing basic support as a sensor integration carrier. Their combination with MEMS sensors has become an important technical path to achieve anthropomorphic fingertip sensing. Currently, force sensors are mainly divided into two categories: one-dimensional force sensors (using flexible pressure sensors) and multi-dimensional force sensors. MEMS three-dimensional force sensors can simultaneously detect composite forces in the X, Y, and Z directions, acquiring complete and accurate force information such as contact posture and force distribution, making them core components for achieving fine-grained operation scenarios. One-dimensional force sensors (flexible pressure sensors) have a simple structure and lower cost, but can only detect pressure or tension in a single direction, serving as auxiliary sensing units for basic contact scenarios. Existing solutions use ordinary three-dimensional force sensors or single flexible pressure sensors, resulting in insufficient detection accuracy, response speed, and space utilization. Furthermore, they are not integrated with flexible pressure sensors, relying solely on a single type of MEMS three-dimensional force sensor, failing to meet both fine-grained detection and basic sensing requirements. When using only ordinary three-dimensional force sensors, not only are the detection accuracy and response speed inferior to MEMS three-dimensional force sensors, but there are also problems such as complex structure, high manufacturing cost, and redundant detection accuracy in some scenarios, which cannot fully adapt to the compact structure of the fingertip. When using only flexible pressure sensors as one-dimensional force sensors, the perception dimension is singular, and it is impossible to obtain complete force information (such as contact posture and force distribution) when the fingertip contacts an object, and it is impossible to achieve anthropomorphic fine force feedback.Existing 3D force sensors often employ a separate deployment (located on different substrates or at different positions on the fingertip), resulting in a loose system structure, large space occupation, and incompatibility with the compact structure of the human fingertip. Furthermore, signal interference is easily induced, further reducing sensing accuracy and leading to errors during precise robotic grasping and posture adjustment. Simultaneously, existing technologies often employ rigid bonding or mechanical fixation, resulting in poor adhesion between the sensor and the flexible substrate. When the fingertip bends or deforms, the sensor is prone to detachment or displacement from the substrate, affecting detection accuracy and shortening the lifespan of the sensing system. The design of the flexible substrate also fails to prioritize the structural requirements of MEMS 3D force sensors, merely satisfying basic flexible adhesion, creating a mismatch between flexibility and sensor rigidity, further limiting the advantages of MEMS 3D force sensors.

[0003] Furthermore, existing flexible pressure sensors, used as one-dimensional force sensors, generally suffer from inherent performance defects, including insufficient stability and mediocre linearity. During long-term, repeated bending and deformation of the fingertip, they are prone to signal drift and increased measurement errors. Existing solutions cannot overcome this deficiency, failing to achieve long-term stable, high-precision force detection, further limiting the improvement of anthropomorphic sensing effects. Additionally, some existing integrated fingertip sensing solutions, in order to achieve multi-dimensional force detection, can only employ complex transmission structures or multi-board splicing designs, resulting in large system size and weight. This is incompatible with the small structure of human fingertips and cannot meet the design requirements of miniaturized, lightweight humanoid robot fingertips. At the same time, the complex structure increases assembly difficulty and manufacturing costs, and makes subsequent maintenance inconvenient, hindering large-scale production and widespread adoption. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-dimensional force sensing device for the fingertips of humanoid robots and its packaging method, in order to solve the problems of existing technologies such as the lack of structural optimization integration methods for existing force sensors, poor adaptability to flexible substrate integration, and insufficient fit and flexibility. This invention uses a flip-chip MEMS three-dimensional force sensor as the core, realizing the integrated integration of the two on the same flexible substrate, giving full play to the spatial and precision advantages of the MEMS flip-chip structure, realizing multi-dimensional force collaborative perception, improving the comprehensiveness and accuracy of fingertip perception, and meeting the needs of robot fine operation.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A multi-dimensional force sensing device for the fingertips of a humanoid robot includes a flip-chip MEMS three-dimensional force sensor, a glass substrate, an upper flexible substrate, a flexible protective layer, a lower flexible substrate, and lead electrodes. The upper flexible substrate is integrated on the lower flexible substrate and lead electrodes, the glass substrate is integrated on the upper flexible substrate, the flip-chip MEMS three-dimensional force sensor is integrated on the glass substrate, and the flip-chip MEMS three-dimensional force sensor, the glass substrate, and the upper flexible substrate are encapsulated on the lower flexible substrate and lead electrodes through the flexible protective layer.

[0006] Preferably, the upper flexible substrate is mechanically connected to the lower flexible substrate and the lead electrode, and the upper flexible substrate, the lower flexible substrate and the lead electrode are interconnected by a conductive material. The flip-chip MEMS three-dimensional force sensor, the glass substrate and the upper flexible substrate are interconnected by a conductive material.

[0007] Preferably, the inverted MEMS three-dimensional force sensor includes a central cylindrical force transmission column, a square mass island, four cantilever beams, and an outer peripheral fixed end. The central cylindrical force transmission column is located at the center of the square mass island, the four cantilever beams are arranged in a circular array around the square mass island, and the outer peripheral fixed end is located on the outside of the square mass island.

[0008] Preferably, the central cylindrical force transmission column serves as the force input end, and the bottom end of the central cylindrical force transmission column is integrated with the square mass island. It is formed by integrated processing using micro-nano manufacturing processes such as ICP etching or RIE etching. The four boundaries of the square mass island are connected to one end of each of the four cantilever beams, and the other end of the cantilever beams is integrated with the outer peripheral fixed end.

[0009] Preferably, the circuit structure integrated on the flip-chip MEMS three-dimensional force sensor includes 12 piezoresistors and 8 metal electrodes. The piezoresistors are arranged in groups of four to form a Wheatstone bridge circuit, with a total of three groups.

[0010] Preferably, the varistor is a two-turn P-type silicon-doped varistor.

[0011] Preferably, the three Wheatstone bridges share a pair of power supply electrodes, including a first electrode and an eighth electrode. The first electrode is connected to the power supply, and the eighth electrode is grounded. The output difference between the seventh electrode and the fourth electrode is the X-direction output; the output difference between the second electrode and the sixth electrode is the Y-direction output; and the output difference between the third electrode and the fifth electrode is the Z-direction output.

[0012] A packaging method for the multi-dimensional force sensing device at the fingertips of the humanoid robot includes the following steps: The MEMS three-dimensional force sensor is bonded to a glass substrate, a conductive paste is filled into the through-hole of the glass substrate and cured, and then metal bumps are prepared on the bottom of the glass substrate by electroplating or screen printing to form a core component of MEMS three-dimensional force integration. Grooves and through holes are fabricated at corresponding positions on the upper substrate. The through holes serve both signal conduction and mechanical interlocking functions and can be directly inserted into the metal protrusion of the MEMS three-dimensional force sensor. At the same time, holes are drilled at specific positions of the circuit on the upper substrate to reserve lead wire guidance channels. FPCB electrodes and leads are fabricated on the lower substrate. The MEMS three-dimensional force sensor is embedded in the groove of the upper substrate. The mechanical interlocking effect of the through hole in the groove of the upper substrate is used to directly insert the MEMS three-dimensional force sensor into the through hole, so that the metal protrusion and the through hole are precisely matched, ensuring that the protrusion and the FPCB electrode of the lower substrate are in close contact. Apply adhesive and fill conductive paste into the through-holes of the upper substrate. After curing, the MEMS three-dimensional force sensor is fixed to the two substrates. The flexible pressure sensor and its corresponding leads are fabricated on the surface of the upper flexible substrate to complete the installation of the auxiliary sensing unit.

[0013] Preferably, a cavity is fabricated on the glass substrate, and a through hole is fabricated at the position corresponding to the MEMS three-dimensional force sensor electrode. After the MEMS three-dimensional force sensor electrode is bonded, a conductive paste is filled into the through hole to guide the electrical signal of the MEMS three-dimensional force sensor to the surface of the glass substrate, thus completing the initial signal export.

[0014] Preferably, the metal underbump fabrication technology in the flip-chip bonding process is used to fabricate multiple raised metal underbumps at the electrode position at the bottom of the glass substrate by electroplating or screen printing, forming an integrated core structure from top to bottom consisting of a MEMS three-dimensional force chip, a glass substrate, and multiple metal underbumps.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention integrates a MEMS three-dimensional force sensing chip with a glass substrate via wafer bonding. A pre-fabricated array of metal bumps is present on the bottom of the substrate, resulting in a small, thin, and highly integrated sensing unit with a compact and regular overall structure, suitable for the confined installation space of humanoid robots' fingertips. Alignment and assembly through-holes are coaxially arranged inside the grooves of the upper flexible substrate, forming a reliable mechanical interlocking and limiting structure by interlocking the metal bumps with the through-holes. Simultaneously, a conductive composite material is quantitatively filled into the through-holes using a dispensing process and cured at a constant temperature. This achieves low-impedance, reliable electrical interconnection between the sensing electrodes and the underlying circuitry, while significantly improving the overall assembly structure's locking strength. Under long-term dynamic stress conditions, it is not prone to loosening or delamination, exhibiting excellent structural reliability.

[0016] Preferably, the present invention is equipped with three sets of independent varistors to form a Wheatstone bridge detection circuit, which can realize independent acquisition and precise decoupling of spatial forces in the X, Y and Z directions, effectively suppress crosstalk between multi-axial force signals, and improve the detection accuracy and real-time stability of multi-dimensional tactile perception of humanoid robots' fingertips.

[0017] This invention employs a double-layer flexible composite substrate to achieve a rigid-flexible integrated heterogeneous design. The upper flexible substrate carries a one-dimensional distributed flexible pressure sensing unit, while the lower flexible substrate prefabricates an integrated FPCB lead circuit layer. The whole structure possesses excellent flexibility and bendability, which can conform to the curved contour of a humanoid robot's fingertip and deform synchronously with the fingertip joint.

[0018] This invention adopts a standardized assembly process of first positioning and assembling the three-dimensional force core sensing unit, and then mass-producing the one-dimensional flexible auxiliary sensing unit. At the same time, cross-layer interconnection vias are opened in the circuit centralized lead-out area to realize the orderly arrangement of the full-channel sensing leads in layers and zones, effectively reducing the density of single-layer wiring, avoiding the problem of cross-coupling interference of leads, and greatly improving the purity and stability of weak sensing signals transmitted over long distances. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a humanoid robot fingertip sensing device based on an inverted MEMS three-dimensional force sensor in an embodiment of the present invention.

[0020] Figure 2 This is an exploded view of the structure of the humanoid robot fingertip sensing device based on an inverted MEMS three-dimensional force sensor in an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of a flip-chip MEMS three-dimensional force chip in an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of the deformation of the structure when a force is applied in the Z-axis direction in an embodiment of the present invention.

[0023] Figure 5 This is a schematic diagram of the stress distribution along the X and Y paths when a force is applied in the Z-axis direction in an embodiment of the present invention.

[0024] Figure 6 This is a schematic diagram of the deformation of the structure when a force is applied in the X-axis or Y-axis direction in an embodiment of the present invention.

[0025] Figure 7 This is a schematic diagram of the stress distribution along the X and Y paths when a force is applied in the X-axis direction in an embodiment of the present invention.

[0026] Figure 8 This is a schematic diagram of the stress distribution along the X and Y paths when a force is applied in the Y-axis direction in an embodiment of the present invention.

[0027] Figure 9 This is a schematic diagram of the back-side device layer and lead electrodes in an embodiment of the present invention.

[0028] Figure 10This is a schematic diagram of a varistor bridge in an embodiment of the present invention.

[0029] Figure 11 This is a schematic diagram of the glass substrate in an embodiment of the present invention.

[0030] Figure 12 This is a schematic diagram of the metal protrusion at the bottom of the glass substrate in an embodiment of the present invention.

[0031] Figure 13 This is a schematic diagram of the upper flexible substrate and flexible pressure sensor in an embodiment of the present invention.

[0032] Figure 14 This is a schematic diagram of the flexible protective layer in an embodiment of the present invention.

[0033] Figure 15 This is a schematic diagram of the lower flexible substrate in an embodiment of the present invention.

[0034] In the figure, 1. Inverted MEMS 3D force sensor; 2. Glass substrate; 3. Upper flexible substrate; 4. Flexible protective layer; 5. Lower flexible substrate and lead electrode; 11. Central cylindrical force transmission column; 12. Square mass island; 13. First cantilever beam; 14. Second cantilever beam; 15. Third cantilever beam; 16. Fourth cantilever beam; 17. Outer peripheral fixed end; 101. First stress concentration region; 102. Second stress concentration region; 103. Third stress concentration region; 104. Fourth stress concentration region; 101. First stress concentration region; 102. Second stress concentration region; 103. Third stress concentration region; 104. Fourth stress concentration region; 131. First varistor; 132. Second varistor; 151. Third varistor; 152. Fourth varistor; 141. Fifth varistor; 142. Sixth varistor; 143. Seventh varistor; 144. Eighth varistor; 161. Ninth varistor; 162. Tenth varistor; 163. Eleventh varistor; 164. Twelfth varistor; 181. First electrode; 182. Second electrode; 183. Third electrode; 184. Fourth electrode; 185. Fifth electrode; 186. Sixth electrode; 187. Seventh electrode; 188. Eighth electrode; 21. Glass substrate cavity; 22. First glass through-hole; 23. Second glass through-hole; 24. Third glass through-hole; 25. Fourth glass through-hole; 26. Fifth glass through-hole; 27. Sixth glass through-hole; 28. Seventh glass through-hole; 29. ​​Eighth glass through-hole; 221. First metal lower protrusion; 231. Second metal lower protrusion; 241. Third metal lower protrusion; 251. Fourth metal lower protrusion; 261. Fifth metal lower protrusion; 271. Sixth metal lower protrusion; 281. Seventh metal lower protrusion; 291. Eighth metal lower protrusion; 31. Flexible substrate groove; 321. First flexible pressure sensor; 322. Second flexible pressure sensor; 323. Third flexible pressure sensor; 324. Fourth flexible pressure sensor; 331. First flexible substrate groove; 332. Second flexible substrate groove; 333. Third flexible substrate groove; 334. Fourth flexible substrate groove; 335. Fifth flexible substrate groove; 336. Sixth flexible substrate groove; 337. Seventh flexible substrate groove; 338. Eighth flexible substrate groove; 341. First flexible substrate through hole; 342. Second flexible substrate through hole; 343. Third flexible substrate through hole; 344. Fourth flexible substrate through hole; 345. Fifth flexible substrate through hole; 346. Sixth flexible substrate through hole; 347. Seventh flexible substrate through hole; 348. Eighth flexible substrate through hole; 41. Flexible protective layer with perforated areas; 51. Circuit lead-out terminal. Detailed implementation methods; To enable those skilled in the art to better understand the present invention, 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0036] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0037] like Figure 1As shown, this invention provides a multi-dimensional force sensing device for the fingertips of a humanoid robot, comprising a flip-chip MEMS three-dimensional force sensor 1, a glass substrate 2, an upper flexible substrate 3, a flexible protective layer 4, a lower flexible substrate, and lead electrodes 5; the upper flexible substrate 3 is integrated on the lower flexible substrate and lead electrodes 5, the glass substrate 2 is integrated on the upper flexible substrate 3, and the flip-chip MEMS three-dimensional force sensor 1 is integrated on the glass substrate 2. The flip-chip MEMS three-dimensional force sensor 1, the glass substrate 2, and the upper flexible substrate 3 are encapsulated on the lower flexible substrate and lead electrodes 5 through the flexible protective layer 4; this invention achieves structural integration and complementary signal sensing through the heterogeneous integration of the flip-chip MEMS three-dimensional force sensor 1 with the flexible protective layer 4, the lower flexible substrate, and the lead electrodes 5, combined with a rigid-flexible assembly structure of a double-layer flexible substrate, a mechanical interlocking positioning structure, and a layered cross-layer wiring system. The upper flexible substrate 3 is mechanically connected to the lower flexible substrate and lead electrode 5. The upper flexible substrate 3, the lower flexible substrate, and the lead electrode 5 are interconnected through conductive materials. The flip-chip MEMS three-dimensional force sensor 1, the glass substrate 2, and the upper flexible substrate 3 are interconnected through conductive materials. The components are physically fixed and electrically connected through a combination of mechanical interlocking, conductive material solidification interconnection, and layered circuit connection. Each functional unit has a clear division of labor and cooperates with each other to complete the high-precision, high-stability, and all-area multi-dimensional tactile perception task of the robot's fingertips. It realizes accurate detection of three-dimensional and one-dimensional forces at the fingertips of humanoid robots, adapting to the needs of anthropomorphic operations such as fine grasping and contact recognition. The specific implementation method is as follows.

[0038] This invention addresses the flexible integration scenario of robot fingertips by adapting and structurally modifying a MEMS 3D force sensor into an integrated structural design. To match the rigid-flexible architecture of the dual-layer flexible substrate and the flexible pressure sensor, an innovative inverted MEMS 3D force sensor is employed. This inverted MEMS 3D force sensor serves as the core sensing element of the entire device, and the overall structure is as follows: Figure 3 As shown. Its core mechanical structure includes a central cylindrical force transmission column 11, a square mass island 12, four cantilever beams (13, 14, 15, 16) and an outer peripheral fixed end 17. The central cylindrical force transmission column 11 is located at the center of the square mass island 12, and the four cantilever beams are arranged in a circular array around the square mass island 12. The outer peripheral fixed end 17 is located on the outside of the four cantilever beams, forming a complete island-beam structure.

[0039] The central cylindrical force transmission column 11 serves as the force input end. The bottom end of the central cylindrical force transmission column 11 is integrated with the square mass island 12. It is integrally formed by micro-nano manufacturing processes such as ICP etching or RIE etching. The four boundaries of the square mass island 12 are connected to one end of the four cantilever beams, and the other ends of the four cantilever beams are integrally connected to the outer peripheral fixed end 17. For example, the square mass island 12 is connected to one end of the first cantilever beam 13 along the positive X direction, and the other end of the first cantilever beam 13 is connected to the outer peripheral fixed end 17, forming an integrally fixed micro-mechanical sensitive structure. The connection method of the second cantilever beam 14, the third cantilever beam 15 and the fourth cantilever beam 16 is similar to the installation connection method of the first cantilever beam 13.

[0040] The specific measurement process for three-dimensional force is as follows: When the central cylindrical force transmission column 11 is subjected to a force in the Z direction, the structural deformation is as follows: Figure 4 As shown, the force is vertically transmitted to the square mass island 12 via the force transmission column, causing a slight vertical displacement of the mass island. This results in uniform stress concentration at the connection roots of the four cantilever beams at the corresponding positions around the bottom of the force transmission column on the back of the mass island. The stress distribution along the X or Y direction path is as follows: Figure 5 As shown; the structure is as follows Figure 9 As shown, when subjected to a force in the Z direction, the corresponding varistor arrangement areas (143, 144, 163, 164) in the Y direction experience stress changes. Two varistor arrangement areas (143, 164) experience tensile stress, and two areas (144, 163) experience compressive stress. Their absolute resistance values ​​change synchronously and linearly. This resistance change is converted into an electrical signal output via a Wheatstone bridge, enabling precise measurement of the Z-direction force. When subjected to a force in the X direction, the structural deformation is as follows... Figure 6 As shown, the central force-transmitting column causes the mass island to undergo offset deformation along the X direction, resulting in two stress concentration zones on the back of the mass island along the X direction. The stress distribution along the X or Y direction path is as follows. Figure 7 As shown, the two cantilever beams on either side of the X-direction experience opposite strains, with one cantilever beam under tension and the other under compression. A set of piezoresistive arrays (131, 132, 151, 152) in the corresponding X-direction area senses the stress changes in different directions, resulting in opposite resistance values. The Wheatstone bridge outputs a corresponding electrical signal based on the resistance difference, completing the detection of the force in the X-direction. Furthermore, there is almost no stress in the Y-direction path, thus achieving decoupling of the X and Y-direction forces. The measurement principle of the Y-direction force is completely symmetrical to that of the X-direction. When subjected to a Y-direction force, the mass island undergoes offset deformation along the Y-direction. The stress distribution along the X or Y-direction path at this time is as follows... Figure 8As shown, the X-direction path is almost stress-free, achieving decoupling of forces in the Y and X directions. Relying on the symmetrical mechanical properties of the island-beam structure and the independent placement of three sets of piezoresistors, crosstalk-free and independently decoupled measurement of forces in the X, Y, and Z directions is achieved, ensuring the accuracy of force detection in each direction. The circuit structure of the flip-chip MEMS three-dimensional force sensor is as follows: Figure 9 As shown, the circuit includes 12 two-turn P-type silicon-doped varistors and 8 metal electrodes. The varistors are grouped into three Wheatstone bridge circuits of four, corresponding to the X, Y, and Z directions respectively. Each group is configured according to a pre-defined circuit rule to acquire force signals in the corresponding direction. Varistors (151, 152, 131, 132) are used to measure force in the X direction; varistors (161, 162, 141, 142) are used to measure force in the Y direction; and varistors (163, 164, 143, 144) are used to measure force in the Z direction. The three Wheatstone bridges share a common pair of power supply electrodes: the first electrode 181 is connected to the power supply, and the eighth electrode 188 is grounded. The output difference between the seventh electrode 187 and the fourth electrode 184 represents the X-direction output; the output difference between the second electrode 182 and the sixth electrode 186 represents the Y-direction output; and the output difference between the third electrode 183 and the fifth electrode 185 represents the Z-direction output. The circuit bridge configuration is as follows: Figure 10 As shown, resistors R1-R12 are twelve two-turn P-type silicon-doped varistors. Four varistors form a group to build a Wheatstone full-bridge circuit, for a total of three groups. These circuits are used to measure forces in the X, Y, and Z directions, respectively. The three Wheatstone full-bridge circuits are connected in parallel to the same DC voltage source. Each bridge consists of two series-connected dual-resistor branches, such as resistors R1 and R2 in series, and resistors R3 and R4 in series. Resistors R1, R2, R3, and R4 together form a Wheatstone full-bridge circuit. The bridge circuit has 12 resistors evenly distributed to three sets of measurement channels. Each set of bridges draws potential signals from the midpoints of two series branches. The differential output voltage of each energized bridge circuit is obtained by collecting the potential difference between the midpoints of the two sets. For example, the potential difference between U1 and U2 is the output voltage of the bridge with resistors R1, R2, R3, and R4. The three sets of bridges share the same excitation power supply, which can realize the synchronous acquisition of force output signals in three directions. Each measurement channel is electrically independent of each other, and can complete three-dimensional force measurement while ensuring that the excitation voltage is consistent.

[0041] Its fabrication and packaging process is closely related to the rigid-flexible bonding structure. The packaging principle of MEMS chips is as follows: The MEMS three-dimensional force sensor is first connected to the glass substrate through a bonding process, such as... Figure 11As shown, this forms an integrated core component. During the glass substrate fabrication process, a cavity 21 is first created on the glass substrate, and through-holes (22, 23, 24, 25, 26, 27, 28, 29) are created at positions corresponding to the MEMS three-dimensional force sensor electrodes. After bonding, conductive paste is filled into these through-holes to guide the electrical signals of the MEMS three-dimensional force sensor to the surface of the glass substrate, completing the initial signal export. Subsequently, using the metal underbump fabrication technology in chip flip-chip bonding, multiple raised metal underbumps are fabricated at the electrode positions on the bottom of the glass substrate using electroplating or screen printing. This ultimately forms an integrated core structure from top to bottom: the MEMS three-dimensional force chip, the glass substrate, and multiple metal underbumps, as shown below. Figure 12 As shown, the metal bumps (221, 231, 241, 251, 261, 271, 281, 291) correspond to the positions of the chip electrodes.

[0042] This device employs a rigid-flexible hybrid structure design to achieve a perfect fit between the core sensor and the flexible substrate. The specific structure and installation method are as follows: The rigid-flexible hybrid structure uses two substrates, both made of PI (polyimide) or PDMS material, balancing flexible deformation capability with structural stability to meet the bending motion requirements of the robot's fingertips. The upper flexible substrate is relatively thicker. The upper substrate and flexible pressure sensor structure are as follows: Figure 13 As shown, a groove 31 is fabricated at the location corresponding to the placement of the MEMS three-dimensional force sensor. This groove is used to limit the position of the MEMS three-dimensional force sensor (including the glass substrate and the metal protrusion), while balancing the overall height to ensure that the height of the MEMS three-dimensional force sensor is similar to that of the subsequent auxiliary sensing unit and that the working surface is flat. An FPCB (flexible printed circuit board) is fabricated on the lower flexible substrate, and the structure of the lower substrate is as follows. Figure 14As shown, electrodes and leads are pre-installed on the FPCB, serving as the core carrier for signal transmission in the entire device. Corresponding to the positions of the MEMS 3D force sensor electrodes, grooves (331, 332, 333, 334, 335, 336, 337, 338) are simultaneously formed within the grooves of the upper flexible substrate. The groove apertures precisely match the dimensions of the metal protrusions at the bottom of the MEMS 3D force sensor. This not only facilitates the precise insertion of the metal protrusions into the grooves and their close contact with the electrodes on the lower FPCB for signal conduction, but also provides a mechanical interlocking function, allowing the MEMS 3D force sensor to be directly inserted into the grooves. After the metal bump is inserted into the groove, conductive material is filled into the through hole by dispensing. After the conductive material cures, it not only achieves stable conduction between the metal bump and the lower substrate FPCB electrode, but also serves to connect and fix the MEMS three-dimensional force sensor (including the glass substrate and the metal bump), the upper substrate, and the lower substrate. Through the synergistic cooperation of the through hole, conductive material, and metal bump, the connection between the MEMS three-dimensional force sensor and the upper substrate is further improved, preventing the sensor from shifting or loosening during stress or deformation.

[0043] The flexible pressure sensor, serving as an auxiliary sensing unit (flexible one-dimensional force unit), works in conjunction with the flip-chip MEMS three-dimensional force sensor. Its fabrication and deployment are as follows: The core sensing layer of the flexible pressure sensor is an MXene / CNTs composite film, tightly bonded and fixed to the surface of the upper flexible substrate, positioned at approximately the same height as the MEMS three-dimensional force sensor. It is arranged around the perimeter of the MEMS three-dimensional force sensor to enhance pressure sensing capability. After the flexible pressure sensor (one-dimensional force unit) and its corresponding lead electrodes are fabricated, a PI or PDMS substrate is applied as the outermost flexible protective layer. Figure 14 This effectively isolates external dust and moisture, protecting the MXene / CNTs composite film and electrodes from damage. For the location of the MEMS three-dimensional force sensor, a hollowed-out area 41 is created on the outermost protective layer. This hollowed-out area precisely matches the dimensions of the MEMS three-dimensional force sensor, ensuring that the central force transmission column of the MEMS three-dimensional force sensor is exposed, allowing it to normally receive external forces and complete force signal acquisition. This ensures the stability of the auxiliary sensing unit without affecting the normal operation of the core sensing unit.

[0044] The electrodes and leads of the MEMS three-dimensional force sensor and the flexible pressure sensor (flexible one-dimensional force unit) for auxiliary measurement are arranged in layers. Most of the leads and electrodes of the MEMS three-dimensional force sensor are arranged on the upper surface of the lower substrate; most of the lead electrodes of the flexible pressure sensor are arranged on the upper surface of the upper substrate. This layered wiring method can effectively reduce the number of leads in a single layer, avoid signal interference caused by lead entanglement, ensure stable signal transmission of each sensor, and provide a foundation for subsequent array design. At the same time, through holes (341, 342, 343, 344, 345, 346, 347, 348) are made at the location of the upper substrate according to the wiring requirements. These through holes are used to guide the leads on the surface of the upper flexible substrate to the lower flexible substrate. After the guidance is completed, the upper layer leads and the FPCB leads of the lower flexible substrate are connected together and then connected to the external circuit module, so that all sensor signals can be uniformly exported from the circuit lead-out terminal 51.

[0045] The entire assembly process of the sensing device incorporates a rigid-flexible structural design and is packaged according to the following steps: The first step is to complete the bonding between the MEMS three-dimensional force sensor and the glass substrate, fill the through holes of the glass substrate with conductive paste and cure it, and then prepare metal bumps on the bottom of the glass substrate by electroplating or screen printing to form the core component of MEMS three-dimensional force integration. The second step is to prepare upper and lower flexible substrates. Grooves and through holes are made at corresponding positions on the upper substrate. The through holes have both signal transmission and mechanical interlocking functions and can be directly inserted into the metal protrusion of the MEMS three-dimensional force sensor. At the same time, holes are drilled at specific positions of the circuit on the upper substrate to reserve lead wire guidance channels. FPCB electrodes and leads are prepared on the lower substrate. The third step is to precisely embed the MEMS three-dimensional force integrated core component into the groove of the upper substrate. Utilizing the mechanical interlocking effect of the through hole in the groove of the upper substrate, the MEMS three-dimensional force sensor is directly inserted into the through hole, so that the metal protrusion and the through hole are precisely matched, ensuring that the protrusion and the FPCB electrode of the lower substrate are in close contact. The fourth step is to apply adhesive and fill the through-holes of the upper substrate with conductive paste. After curing, the MEMS three-dimensional force sensor is fixed to the two substrates. The fifth step is to fabricate the flexible pressure sensor (flexible one-dimensional force unit) and corresponding leads on the surface of the upper flexible substrate to complete the installation of the auxiliary sensing unit. The sixth step involves guiding the leads on the surface of the upper flexible substrate to the FPCB leads of the lower substrate through the reserved through holes near the lead-out terminals of the upper substrate circuit, thereby achieving layered lead arrangement. Then, the upper and lower lead wires are connected together to connect to the external circuit module. The seventh step involves encapsulating the entire device, sealing all through-holes and joints to ensure secure connections and good sealing of all components. This prevents issues such as detachment, displacement, or signal interference under stress, ultimately assembling a composite sensing device adapted to the fingertips of humanoid robots. Subsequently, the sensing devices can be arrayed according to actual needs to further improve the omnipresence and accuracy of fingertip sensing.

Claims

1. A multi-dimensional force sensing device for the fingertips of a humanoid robot, characterized in that, The device includes a flip-chip MEMS three-dimensional force sensor (1), a glass substrate (2), an upper flexible substrate (3), a flexible protective layer (4), a lower flexible substrate, and lead electrodes (5). The upper flexible substrate (3) is integrated on the lower flexible substrate and lead electrodes (5), the glass substrate (2) is integrated on the upper flexible substrate (3), the flip-chip MEMS three-dimensional force sensor (1) is integrated on the glass substrate (2), and the flip-chip MEMS three-dimensional force sensor (1), the glass substrate (2), and the upper flexible substrate (3) are encapsulated on the lower flexible substrate and lead electrodes (5) through the flexible protective layer (4).

2. The humanoid robot fingertip multidimensional force sensing device according to claim 1, characterized in that, The upper flexible substrate (3) is mechanically connected to the lower flexible substrate and lead electrode (5). The upper flexible substrate (3) and the lower flexible substrate and lead electrode (5) are interconnected by conductive materials. The flip-chip MEMS three-dimensional force sensor (1), glass substrate (2) and upper flexible substrate (3) are interconnected by conductive materials.

3. The humanoid robot fingertip multidimensional force sensing device according to claim 1, characterized in that, The inverted MEMS three-dimensional force sensor (1) includes a central cylindrical force transmission column (11), a square mass island (12), four cantilever beams and an outer peripheral fixed end (17). The central cylindrical force transmission column (11) is located at the center of the square mass island (12), and the four cantilever beams are arranged in a circular array around the square mass island (12). The outer peripheral fixed end (17) is located on the outside of the square mass island (12).

4. The humanoid robot fingertip multidimensional force sensing device according to claim 3, characterized in that, The central cylindrical force transmission column (11) serves as the force input end. The bottom end of the central cylindrical force transmission column (11) is integrated with the square mass island. It is formed by integrated processing using micro-nano manufacturing process ICP etching or RIE etching. The four boundaries of the square mass island are connected to one end of the four cantilever beams respectively. The other end of the cantilever beam is integrated with the outer peripheral fixed end (17).

5. The humanoid robot fingertip multidimensional force sensing device according to claim 3, characterized in that, The circuit structure integrated on the flip-chip MEMS three-dimensional force sensor (1) includes 12 piezoresistors and 8 metal electrodes. The piezoresistors are arranged in groups of four to build a Wheatstone bridge circuit, and a total of three groups are set up.

6. The humanoid robot fingertip multidimensional force sensing device according to claim 5, characterized in that, The varistor is a two-turn P-type silicon-doped varistor.

7. The humanoid robot fingertip multidimensional force sensing device according to claim 5, characterized in that, The three Wheatstone bridges share a pair of power supply electrodes, including the first electrode (181) and the eighth electrode (188). The first electrode (181) is connected to the power supply, and the eighth electrode (188) is grounded. The output difference between the seventh electrode (187) and the fourth electrode (184) is the X-direction output; the output difference between the second electrode (182) and the sixth electrode (186) is the Y-direction output; and the output difference between the third electrode (183) and the fifth electrode (185) is the Z-direction output.

8. A packaging method for the multi-dimensional force sensing device for the fingertips of a humanoid robot as described in claim 1, characterized in that, Includes the following steps: The MEMS three-dimensional force sensor is bonded to a glass substrate, a conductive paste is filled into the through-hole of the glass substrate and cured, and then metal bumps are prepared on the bottom of the glass substrate by electroplating or screen printing to form a core component of MEMS three-dimensional force integration. Grooves and through holes are fabricated at corresponding positions on the upper substrate. The through holes serve both signal conduction and mechanical interlocking functions and can be directly inserted into the metal protrusion of the MEMS three-dimensional force sensor. At the same time, holes are drilled at specific positions of the circuit on the upper substrate to reserve lead wire guidance channels. FPCB electrodes and leads are fabricated on the lower substrate. The MEMS three-dimensional force sensor is embedded in the groove of the upper substrate. The mechanical interlocking effect of the through hole in the groove of the upper substrate is used to directly insert the MEMS three-dimensional force sensor into the through hole, so that the metal protrusion and the through hole are precisely matched, ensuring that the protrusion and the FPCB electrode of the lower substrate are in close contact. Apply adhesive and fill conductive paste into the through-holes of the upper substrate. After curing, the MEMS three-dimensional force sensor is fixed to the two substrates. The flexible pressure sensor and its corresponding leads are fabricated on the surface of the upper flexible substrate to complete the installation of the auxiliary sensing unit.

9. The packaging method of the humanoid robot fingertip multidimensional force sensing device according to claim 8, characterized in that, A cavity is fabricated on a glass substrate, and a through hole is fabricated at the position corresponding to the MEMS three-dimensional force sensor electrode. After the MEMS three-dimensional force sensor electrode is bonded, a conductive paste is filled into the through hole to guide the electrical signal of the MEMS three-dimensional force sensor to the surface of the glass substrate, thus completing the initial signal export.

10. The packaging method of the humanoid robot fingertip multidimensional force sensing device according to claim 8, characterized in that, Using the metal underbump fabrication technology in the flip-chip bonding process, multiple raised metal underbumps are fabricated at the electrode position at the bottom of the glass substrate by electroplating or screen printing, forming an integrated core structure from top to bottom consisting of a MEMS three-dimensional force chip, a glass substrate, and multiple metal underbumps.

Images