A dexterous fingertip with multi-point tactile perception

Abstract

The present invention discloses a dexterous fingertip with multi-point tactile perception, including a piezoresistive tactile sensing unit, the sensing unit including a substrate, an array electrode attached to the substrate, a piezoresistive layer arranged above the array electrode, a plastic sealing layer for fixing the substrate and the piezoresistive layer, a pre-pressing pad attached above the plastic sealing layer, a silicone contact layer arranged above the pre-pressing pad, and a fingertip base and a fingertip splint that encapsulate the sensing unit as a whole, wherein the silicone contact layer is provided with array contacts corresponding to the array electrodes. The dexterous fingertip can realize the detection of multi-point contact force, has a low manufacturing cost, and has excellent sensitivity.

Description

Technical Field

[0001] The invention relates to the field of robot sensing technology, and in particular to a dexterous fingertip with multi-point tactile perception and a preparation method thereof. Background Art

[0002] When a robot performs a complex operation task, it often obtains information about the surrounding environment through various sensors, the most common of which are visual sensors and tactile sensors. Due to the growing development of computer vision and image processing technology, visual sensors have been widely equipped and used by robots. However, visual sensing technology still faces many difficulties and challenges. For example, visual sensors cannot perform their performance in complex environments with dim light and many background interferences. Secondly, visual sensing technology cannot obtain physical characteristics such as stiffness, texture, weight and hardness of objects. Therefore, it has become a current development trend to install high-performance tactile sensors for robots to explore the environment and identify objects. At the same time, with the emergence of new excellent conductive materials such as graphene and multi-walled carbon nanotubes, tactile sensors are gradually developing towards high sensitivity, high array and flexibility. This also provides the possibility for robots to achieve tactile perception capabilities close to those of humans.

[0003] Although there are many solutions for fingertip tactile sensors, there are still few tactile sensors that can be actually used in the fingertips of robots to assist in daily operations. Traditional fingertip sensors are mostly made of metal, which are large in size and difficult to integrate into the fingertips of dexterous hands. Moreover, most of them are single-point type, which can collect less fingertip information and cannot meet the exploration needs of dexterous hands. Therefore, the development of flexible array tactile sensors with high sensitivity, good stability and fully integrated into the fingertips of dexterous hands is still an urgent challenge. Summary of the invention

[0004] In order to overcome the technical problems of low array, low sensitivity, low integration and high manufacturing cost of fingertip contact sensors in the prior art, the present invention provides a dexterous fingertip with multi-point tactile perception and a preparation method thereof. The fingertip is encapsulated with an array tactile sensor, which can realize multi-point contact force detection and has a low manufacturing cost, laying a foundation for the subsequent dexterous operation of multi-dexterous hands.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A dexterous fingertip with multi-point tactile perception includes a piezoresistive tactile sensing unit, which includes a substrate, an array electrode attached to the substrate, a piezoresistive layer arranged above the array electrode, a plastic sealing layer for fixing the substrate and the piezoresistive layer, a pre-pressing gasket attached above the plastic sealing layer, a silicone contact layer arranged above the pre-pressing gasket, and a fingertip base and a fingertip splint that encapsulate the sensing unit as a whole, wherein the silicone contact layer is provided with array contacts corresponding to the array electrodes.

[0007] Furthermore, the substrate is made of a polyimide film, and the array electrodes are printed on the polyimide film.

[0008] Furthermore, an installation groove is reserved on the top of the fingertip base for placing the sensor unit, and a slide groove is provided on the fingertip base for installing a fingertip splint; array holes are reserved on the fingertip splint corresponding to the array electrodes, so that the contacts of the silicone contact layer are exposed on the fingertip surface, and the fingertip splint is fixed to the fingertip base by a buckle, so that the sensor unit will not be offset and has a certain pre-pressure.

[0009] Furthermore, the piezoresistive layer is made of velostat conductive film.

[0010] Furthermore, the array electrode includes a common electrode and other electrodes arranged in an array, the common electrode is connected to the GND terminal, and the other electrodes are connected to the positive electrode of the power supply. When the sensor unit is subjected to pressure, the piezoresistive material in the corresponding area connects the electrode and the common electrode to form a conductive path with resistance, and the size of the resistance is inversely proportional to the pressure.

[0011] Furthermore, the silicone in the pre-compression gasket and the silicone contact layer are both made of Ecoflex 0030 two-component liquid platinum silicone.

[0012] Furthermore, the preparation method of the silicone contact layer includes: using a mold with a hemispherical cavity array, pouring a uniformly mixed mixture of silicone and glass beads into the mold, extracting bubbles in the mixture under a negative pressure of 0.1 MPa, and demolding after curing to form a flexible contact layer, wherein the mass fraction of the glass microspheres in the silicone is 5%.

[0013] Furthermore, the fingertip base and the fingertip splint are both processed by 3D printing, and the material thereof is epoxy resin.

[0014] In summary, the present invention has the following beneficial effects:

[0015] (1) High integration and small size, no additional connectors are required during installation;

[0016] (2) The fingertip sensor can detect multi-point contact force and has a low manufacturing cost;

[0017] (3) By setting a silicone pre-pressure gasket, the sensor can have a certain initial pre-pressure, skipping the nonlinear interval in the initial stage, which is beneficial to improving the detection sensitivity;

[0018] (4) Adding a specific amount of glass beads to the silicone contact layer can effectively increase the elastic modulus of the contact layer, so that the contact force of the sensor can be better transmitted to the sensing unit when it contacts an object, thereby improving the sensitivity of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall packaging explosion of the piezoresistive flexible array tactile sensor in the present invention.

[0020] Figure 2 It is a diagram of the sensor electrode structure of the present invention.

[0021] Figure 3 It is a left view of the fingertip base of the sensor in the present invention.

[0022] Figure 4 The figure is a comparison of the pressure characteristic curves of the sensor with and without the pre-compression gasket in the present invention.

[0023] In the figure:

[0024] Fingertip splint 1, silicone contact layer 2, silicone pre-compression gasket 3, plastic sealing film 4, velostat piezoresistive film 5, electrode layer 6, fingertip base 7, common terminal electrode 8, array electrode 9, and bottom slide groove 10 of fingertip base. DETAILED DESCRIPTION

[0025] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0026] The dexterous fingertips with multi-point tactile perception of the present invention include a piezoresistive tactile sensing unit, which includes a substrate, an array electrode attached to the substrate, a piezoresistive layer arranged above the array electrode, a plastic sealing layer for fixing the substrate and the piezoresistive layer (that is, the piezoresistive layer material and the electrode are completely fitted through the encapsulation of the plastic sealing layer), a pre-pressing gasket attached above the plastic sealing layer, a silicone contact layer arranged above the pre-pressing gasket, and a fingertip base and a fingertip splint that encapsulate the sensing unit as a whole, and the silicone contact layer is provided with array contacts corresponding to the array electrodes.

[0027] In a specific embodiment of the present invention, the array electrode includes 9 array-arranged electrodes and 1 common electrode, and the piezoresistive material is covered on the electrode layer, wherein the 9 array electrodes are connected to the positive pole of the power supply, and the 1 common electrode is connected to the GND end. When the sensing unit is subjected to pressure, the piezoresistive material in the corresponding area will connect the array electrode and the common electrode to form a conductive path with a certain resistance value, and the resistance value is inversely proportional to the pressure. The piezoresistive layer material can be selected from velostat conductive film, which has excellent piezoresistive properties and is cut into the same shape as the electrode layer.

[0028] In a specific embodiment of the present invention, the pre-compression gasket is a silicone pre-compression gasket. The pre-compression gasket can make the sensor have a certain initial pre-compression, thereby effectively shortening the response time and improving the sensitivity.

[0029] In a specific embodiment of the present invention, the silicone contact layer is made of a mixture of silicone and glass beads to greatly improve the sensitivity of the sensor.

[0030] Example:

[0031] This embodiment provides a dexterous fingertip design with multi-point tactile perception, and its structure is as follows Figure 1 As shown: the fingertip includes an array-arranged piezoresistive tactile sensing unit, which includes a polyimide film as a substrate, a common terminal electrode and an array electrode attached to the substrate, a piezoresistive layer fixed above the substrate, a plastic sealing layer for fixing the substrate and the piezoresistive layer, a pre-pressing gasket attached above the plastic sealing layer, a silicone contact layer fixed above the pre-pressing gasket, and a fingertip base and a fingertip splint that encapsulate the sensing unit as a whole.

[0032] exist Figure 1 In the fingertip structure, the electrode structure diagram of the array-arranged piezoresistive flexible array tactile sensor unit is as follows Figure 2 As shown: a common terminal electrode and a 3×3 array electrode are attached to the substrate, wherein the common terminal electrode 8 is used for grounding, and the array electrode 9 is connected to a multiplexing switch and connected to the positive electrode in turn by a time-division multiplexing method.

[0033] The right side view of the fingertip base is as follows Figure 3 As shown, two slide grooves are designed at the bottom of the base for fixing the fingertip splint in the form of a snap. This fixing method eliminates the need for connectors and is simple to install and disassemble.

[0034] As an improvement, the substrate is provided with electrical lead-out portions for each electrode, and the electrodes of each pressure sensing unit are led out to the outside, so as to facilitate circuit connection between each pressure sensing unit and the outside.

[0035] The working principle of the piezoresistive flexible array tactile sensor based on the above structure is as follows: when the tactile sensor is not subjected to pressure, the piezoresistive film 5 is only subjected to the initial pre-pressure between the fingertip splint 1 and the fingertip base 7, and the resistance of the piezoresistive film is the initial resistance. When the sensor contacts an external object, the spherical contact of the silicone contact layer 2 is deformed, and the contact transmits the force received to the piezoresistive film 5. Due to the characteristics of the piezoresistive material, the resistance of the piezoresistive film decreases after being subjected to pressure, and the current in the circuit becomes larger. However, since the single-chip microcomputer cannot directly measure the current signal in the loop, a voltage-dividing resistor R is connected in series after the sensing unit, and its voltage is measured by the single-chip microcomputer to reflect the pressure signal received. The greater the pressure on the flexible contact, the greater the voltage of the voltage-dividing resistor, until the resistance of the piezoresistive material reaches the minimum value, at which time the pressure sensing unit also reaches the maximum range of pressure monitoring.

[0036] When the pressure acting on the tactile sensor is released, the conductive path in the piezoresistive material will return to its initial state, its resistance will also return to its initial value, and the electrical signal output by the tactile sensing unit will also return to its initial value when there is no external pressure.

[0037] Since the sensor has multiple sensing contacts forming an array, in order to save the occupancy of the microcontroller acquisition peripherals, a multiplexer is used to cyclically select the acquisition unit. The multiplexer's single input terminal is connected to the positive pole of the power supply, and the multiple output terminals are connected to each sensing unit. Therefore, each time the acquisition is performed, a sensing unit forms a complete acquisition loop. Since the clock frequency of the microcontroller is extremely high, it can be regarded as almost simultaneous acquisition of all sensing units.

[0038] On the other hand, this embodiment also provides a method for preparing the above-mentioned sensor. First, the electrode layer is prepared by sputtering a copper film on a polyimide film substrate using a metal sputtering method to form a Figure 4 The common electrodes and array electrodes are laid out, and the lead-out parts of each electrode are formed by sputtering in the same way.

[0039] The piezoresistive layer and the electrode layer are then packaged, and a plastic film is covered under the electrode substrate and over the piezoresistive film. Then, under the heating of a plastic sealing machine, the plastic film is thermally bonded and the electrode substrate is completely fitted with the piezoresistive material.

[0040] Next, the flexible contact layer 2 and the silicone pre-pressed gasket 3 are prepared. The two are respectively injected using molds A and B, using Ecoflex0030 two-component liquid platinum silicone. The two-component room temperature curing platinum catalyzed silicone rubber prepared in a 1:1 ratio is mixed and injected into molds A and B. Mold A has a hemispherical cavity array, and mold B is a membrane cavity. The bubbles in the platinum catalyzed silicone rubber are extracted under a negative pressure of 0.1MPa and maintained for 5 minutes. Then the mold containing silicone is placed in an oven and heated at 50°C for 2 hours. Finally, the mold is taken out and cooled and demolded to complete the preparation of the flexible contact and pre-pressed gasket. When preparing the flexible contact, glass beads with a mass fraction of 5% are added to the evenly mixed silicone and mixed before being injected into mold A. The flexible contact prepared in this way can have a better elastic modulus and improve the sensitivity of the sensor.

[0041] pass Figure 4 It can be seen that the pressure characteristic curve of the sensor without the pre-load gasket can be roughly divided into three stages. The sensitivity of the first and third stages is high, but the sensitivity of the middle stage is low, and the linearity of the three stages is very low, which is difficult to fit with common linear or polynomial curves. Therefore, in order to skip the first and second stages, a pre-load gasket is installed inside the sensor. It can be seen that the pressure characteristic curve of the sensor with pre-load is similar to a binomial curve and has a high sensitivity.

[0042] The fingertip pressure sensor based on the above structure and preparation method has the following advantages: (1) High integration and small size, no additional connectors are required during installation. (2) The fingertip sensor can detect multi-point contact force and has low manufacturing cost; (3) The sensor can have a certain initial pre-pressure through the silicone pre-pressure gasket, skipping the nonlinear interval in the initial stage; (4) A certain amount of glass beads is added to the silicone contact layer to increase the elastic modulus of the contact layer, so that the contact force of the sensor can be better transmitted to the sensing unit when it contacts the object, thereby improving the sensitivity of the sensor.

[0043] It should be noted that the above embodiments are only detailed descriptions of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, there will be changes in the specific implementation methods based on the ideas provided by the present invention, and these changes should also be regarded as the scope of protection of the present invention.

Claims

1. A dexterous fingertip with multi-point tactile perception, characterized in that: The invention comprises a piezoresistive tactile sensor unit, which comprises a substrate, an array electrode attached to the substrate, a piezoresistive layer arranged above the array electrode, a plastic sealing layer for fixing the substrate and the piezoresistive layer, a pre-pressing gasket attached above the plastic sealing layer, a silicone contact layer arranged above the pre-pressing gasket, and a fingertip base and a fingertip splint for integrally packaging the sensor unit, wherein the silicone contact layer is provided with array contacts corresponding to the array electrode; an installation groove is reserved on the top of the fingertip base for placing the sensor unit, and a slide groove is provided on the fingertip base for installing the fingertip splint; the fingertip splint Array holes are reserved on the board corresponding to the array electrodes, so that the contacts of the silicone contact layer are exposed on the surface of the fingertip, and the fingertip splint is fixed to the fingertip base by a buckle, so that the sensor unit will not be offset and has a certain pre-pressure; the array electrode includes a common electrode and other electrodes arranged in an array, the common electrode is connected to the GND terminal, and the other electrodes are connected to the positive electrode of the power supply. When the sensor unit is subjected to pressure, the piezoresistive material in the corresponding area connects the electrode and the common electrode to form a conductive path with a resistance value, and the size of the resistance value is inversely proportional to the size of the pressure; The preparation method of the silicone contact layer includes: using a mold with a hemispherical cavity array, pouring a uniformly mixed mixture of silicone and glass beads into the mold, extracting bubbles in the mixture under a negative pressure of 0.1 MPa, and demolding after curing to form a flexible contact layer, wherein the mass fraction of the glass microspheres in the silicone is 5%.

2. The dexterous fingertip with multi-point tactile perception according to claim 1, characterized in that: The substrate is made of a polyimide film, and the array electrodes are printed on the polyimide film.

3. The dexterous fingertip with multi-point tactile perception according to claim 1, characterized in that: The piezoresistive layer is made of velostat conductive film.

4. The dexterous fingertip with multi-point tactile perception according to claim 1, characterized in that: The silicone in the pre-compression gasket and the silicone contact layer are both made of Ecoflex0030 two-component liquid platinum silicone.

5. The dexterous fingertip with multi-point tactile perception according to claim 1, characterized in that: The fingertip base and the fingertip splint are both processed by 3D printing, and the material thereof is epoxy resin.

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