CN115139322A - Dexterous fingertip with multi-point touch perception - Google Patents

Abstract

The invention discloses a dexterous fingertip with multi-point tactile perception, comprising a piezoresistive tactile sensing unit. The sensing unit includes an array electrode as a substrate, an array electrode attached to the substrate, and a piezoresistive layer arranged above the array electrode. , The plastic sealing layer used to fix the substrate and the piezoresistive layer, the pre-pressing gasket attached to the plastic sealing layer, the silicone contact layer above the pre-pressing gasket, and the fingertip base and the fingertip base that encapsulate the sensing unit as a whole. A sharp splint, the silica gel 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 low manufacturing cost, and has excellent sensitivity.

Description

A dexterous fingertip with multi-point tactile perception

technical field

The invention relates to the technical field of robot sensing, in particular to a dexterous fingertip with multi-point tactile perception and a preparation method thereof.

Background technique

When a robot performs a complex operation task, it often obtains surrounding environment information through various sensors, the most common being visual sensors and tactile sensors. Due to the increasing development of computer vision and image processing technology, vision sensors have been widely used in robots. However, visual sensing technology still faces many difficulties and challenges. For example, visual sensors cannot exert their performance in complex environments with dim light and many background disturbances. Second, visual sensing technology is also unable to capture physical characteristics such as stiffness, texture, weight, and hardness of an object. 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 in the direction of high sensitivity, high array and flexibility. This also provides the possibility for robots to achieve tactile perception capabilities that are close to humans.

Although there are many solutions for fingertip tactile sensors, there are still few tactile sensors that can be practically applied to robotic fingertips for daily operation assistance. Most of the traditional fingertip sensors are metal products, which are large in size and difficult to integrate into the fingertips of dexterous hands; and most of them are single-point types, which can collect less fingertip information and cannot meet the exploration needs of dexterous hands. Therefore, the development of flexible array tactile sensors that are highly sensitive, stable, and fully integrated into the dexterous fingertip remains an urgent challenge.

SUMMARY OF THE INVENTION

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. An array type tactile sensor is encapsulated in the inner package, which can realize the detection of multi-point contact force and has a low manufacturing cost, which lays a foundation for the subsequent multi-dexterous hand to realize dexterous operation.

In order to achieve the above object, the technical scheme adopted in the present invention is:

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

Further, the substrate adopts a polyimide film, and the array electrodes are printed on the polyimide film.

Further, a mounting slot is reserved on the top of the fingertip base for placing the sensor unit, and a chute is provided on the fingertip base for the installation of the fingertip splint; The electrodes correspond, 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 through the buckle, so that the sensor unit does not shift and has a certain pre-pressure.

Further, the piezoresistive layer is selected from velostat conductive film.

Further, the array electrodes include a common electrode and other electrodes arranged in an array. The common electrode is connected to the GND terminal, and the remaining 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 is connected to the electrode and the common electrode. Thus, a conductive path with resistance is formed, and the resistance is inversely proportional to the pressure.

Further, the pre-pressing gasket and the silica gel in the silica gel contact layer are all made of Ecoflex0030 two-component liquid platinum silica gel.

Further, the preparation method of the silicone contact layer includes: using a mold with a hemispherical cavity array, pouring a uniformly mixed mixture of silica gel and glass microbeads into the mold, and extracting the mixture under a negative pressure of 0.1 MPa. Bubble, demoulding after curing to form a flexible contact layer, and the mass fraction of glass microspheres in silica gel is 5%.

Further, both the fingertip base and the fingertip splint are processed by 3D printing, and the material is epoxy resin.

To sum up, the present invention has the following beneficial effects:

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

(2) The fingertip sensor can realize the detection of multi-point contact force and has low manufacturing cost;

(3) By setting the pre-pressure gasket of silica gel, the sensor can have a certain initial pre-pressure, skip the nonlinear interval in the initial stage, which is beneficial to improve the sensitivity of detection;

(4) Adding a specific amount of glass beads to the silicone contact layer can effectively improve 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, which improves the sensor's performance. sensitivity.

Description of drawings

FIG. 1 is a schematic diagram of the overall package explosion of the piezoresistive flexible array tactile sensor of the present invention.

FIG. 2 is a structural diagram of the sensor electrode in the present invention.

Figure 3 is a left side view of the sensor fingertip base in the present invention.

FIG. 4 is a comparison of the pressure characteristic curves of the sensor with or without the preload gasket in the present invention.

In the picture:

Fingertip splint 1, silicone contact layer 2, silicone pre-pressed gasket 3, plastic film 4, velostat piezoresistive film 5, electrode layer 6, fingertip base 7, common terminal electrode 8, array electrode 9, fingertip Base bottom chute 10.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, only used to explain the present invention, and should not be construed as a limitation of the present invention.

The dexterous fingertip with multi-point tactile perception of the present invention includes a piezoresistive tactile sensing unit, the sensing unit includes as a substrate, an array electrode attached to the substrate, a piezoresistive layer disposed above the array electrode, a The plastic sealing layer that fixes the substrate and the piezoresistive layer (that is, the piezoresistive layer material and the electrode are completely attached by the packaging of the plastic sealing layer), the pre-pressing gasket attached to the plastic sealing layer, and the silicone contact above the pre-pressing gasket layer and the fingertip base and 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.

In a specific embodiment of the present invention, the array electrodes include 9 electrodes arranged in an array and 1 common electrode, the piezoresistive material is covered on the electrode layer, wherein 9 array electrodes are connected to the positive electrode of the power supply, and 1 common electrode is connected to At the GND end, when the sensing unit is under 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 The material can be selected from velostat conductive film, which has excellent piezoresistive properties, and is cut into the same shape as the electrode layer.

In a specific embodiment of the present invention, the pre-compressed gasket is a silicone pre-compressed gasket, and the use of the pre-compressed gasket can make the sensor have a certain initial pre-pressure, thereby effectively shortening the response time and improving the sensitivity.

In a specific embodiment of the present invention, the silica gel contact layer is made of a mixture of silica gel and glass microbeads, so as to greatly improve the sensitivity of the sensor.

Example:

This embodiment provides a dexterous fingertip design with multi-point tactile perception, the structure of which is shown in Figure 1: the fingertip includes piezoresistive tactile sensing units arranged in an array, and the sensing unit includes a substrate as a substrate Polyimide film, common terminal electrode and array electrode attached to the substrate, piezoresistive layer fixed above the substrate, plastic sealing layer used to fix the substrate and the piezoresistive layer, pre-compressed gasket attached to the plastic sealing layer, The silicone contact layer fixed on the pre-pressed gasket and the fingertip base and fingertip splint that encapsulate the sensing unit as a whole.

In the fingertip structure of Figure 1, the schematic diagram of the electrode structure in the piezoresistive flexible array tactile sensing unit arranged in an array is shown in Figure 2: A common terminal electrode and a 3×3 array of electrodes are attached to the substrate , wherein the common terminal electrode 8 is used for grounding, and the array electrode 9 is connected to the multiplexing switch, and is connected to the positive electrode in turn by the method of time division multiplexing.

The right view of the fingertip base is shown in Figure 3. Two sliding grooves are designed at the bottom of the base to be fastened to the fingertip splint in the form of a snap. This fixing method eliminates the need for connectors and is easy to install and remove.

As an improvement, there is also an electrical lead-out portion for each electrode on the base plate, which leads the electrode of each pressure sensing unit to the outside, so that each pressure sensing unit can be connected to the outside by a circuit.

The working principle of the piezoresistive flexible array tactile sensor based on the above structure is as follows: when the tactile sensor is not under pressure, the piezoresistive film 5 is only subjected to the initial pre-pressure between the fingertip splint 1 and the fingertip base 7. The resistance of the piezoresistive film is the initial resistance. When the sensor touches an external object, the spherical contact of the silicone contact layer 2 is deformed, and the contact will transmit the force to the piezoresistive film 5. Due to the characteristics of the piezoresistive material, the resistance of the piezoresistive film decreases after being pressed. The current in the circuit becomes larger, but 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 the 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, and the pressure sensing unit also reaches the maximum range of pressure monitoring.

When the pressure applied to 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 return to its original state when there is no external pressure. initial value.

Since the sensor has multiple sensing contacts to form an array, in order to save the occupancy of the acquisition peripherals of the single-chip microcomputer, a multiplexer is used to cyclically select the acquisition unit. Each sensing unit, so each acquisition has a sensing unit to form a complete acquisition loop. Due to the extremely high clock frequency of the single-chip microcomputer, it can be considered that all sensing units are collected at the same time.

On the other hand, this embodiment also provides a method for preparing the above sensor. First, an electrode layer is prepared and a metal sputtering method is used to sputter a copper film on a polyimide film substrate to form the common electrodes and The array electrodes are formed by sputtering in the same way to form the lead-out portions of each electrode.

Then, the piezoresistive layer and the electrode layer are encapsulated, and a plastic encapsulation film is covered under the electrode substrate and above the piezoresistive film. Then, under the heating of the plastic encapsulation machine, the plastic encapsulation film is thermally adhered and the electrode substrate and the piezoresistive material are completely bonded.

Next, prepare the flexible contact layer 2 and the silicone pre-compression gasket 3, which are respectively injection-molded with molds A and B, using Ecoflex0030 two-component liquid platinum silicone. The two-component room temperature-curing platinum-catalyzed silicone rubber prepared in the ratio of 1:1 was mixed and injected into the molds A and B. The mold A had a hemispherical cavity array, and the mold B had a film-like cavity, which was pumped under a negative pressure of 0.1MPa. Remove the air bubbles in the platinum-catalyzed silicone rubber and keep it for 5 minutes, then put the mold containing the silicone in an oven and heat it at 50 °C for 2 hours, and finally take out the mold and cool it. Preparation of tablets. In the preparation of flexible contacts, glass beads with a mass fraction of 5% are added to the uniformly mixed silica gel for mixing and then injected into the A mold. The flexible contacts thus obtained can have better elastic modulus and can improve the sensor. sensitivity.

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

The fingertip pressure sensor based on the above structure and preparation method has the following advantages: (1) The integration is high and the volume is small, and no additional connecting parts are required during installation. (2) The fingertip sensor can realize the detection of multi-point contact force and the manufacturing cost is low; (3) The sensor can have a certain initial pre-pressure through the silicone pre-compression gasket, skipping the nonlinear interval in the initial stage ; (4) A certain amount of glass microbeads are added to the silicone contact layer to improve 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, and the sensitivity of the sensor is improved. .

It should be noted that the above-mentioned embodiments merely describe the preferred embodiments and principles of the present invention in detail. For those of ordinary skill in the art, according to the ideas provided by the present invention, there will be changes in the specific embodiments. And these changes should also be regarded as the protection scope of the present invention.

Claims (8)

1. The utility model provides a dexterous fingertip with multiple spot tactile sensation, its characterized in that, includes piezoresistive tactile sensing unit, and this sensing unit is including as the base plate, attached to the array electrode on the base plate, locating the piezoresistive layer of array electrode top, the plastic envelope layer that is used for fixed substrate and piezoresistive layer, attached to the pre-compaction gasket of plastic envelope layer top, locating the silica gel contact layer of pre-compaction gasket top and with the whole fingertip base and the fingertip splint of encapsulation of sensing unit, be equipped with the array contact on the silica gel contact layer with the array electrode corresponds.

2. The smart fingertip of claim 1, wherein the substrate is a polyimide film, and the array electrodes are printed on the polyimide film.

3. The smart fingertip with multi-point tactile sensation according to claim 1, wherein a mounting groove is reserved at the top of the fingertip base for placing a sensor unit, and a sliding groove is formed in the fingertip base for mounting a fingertip clamping plate; an array hole is reserved on the fingertip clamping plate and corresponds to the array electrode, so that a contact of the silica gel contact layer is exposed out of the surface of a fingertip, and the fingertip clamping plate is fixed with the fingertip base through a buckle, so that the sensor unit cannot deviate and has certain pre-pressure.

4. The smart fingertip of claim 1, wherein the piezoresistive layer is a velostat conductive film.

5. The smart finger tip with multi-touch sensing function according to claim 1, wherein the array electrode comprises a common electrode and the rest of the electrodes arranged in an array, the common electrode is connected to the GND terminal, the rest of the electrodes are connected to the positive electrode of the power supply, when the sensor unit is pressed, the piezoresistive material in the corresponding region connects the electrodes and the common electrode to form a conductive path with a resistance value, and the magnitude of the resistance value is inversely proportional to the magnitude of the pressure.

6. The dexterous fingertip of claim 1, wherein the pre-pressing pad and the silicone in the silicone contact layer are both Ecoflex0030 two-component liquid platinum-gold silicone.

7. The smart fingertip of claim 1, wherein the silicone contact layer is formed by a method comprising: and pouring the uniformly mixed silica gel and glass microsphere mixture into a mold by using the mold with a hemispherical cavity array, pumping out bubbles in the mixture under the negative pressure of 0.1MPa, curing, demolding to form a flexible contact layer, wherein the mass fraction of the glass microspheres in the silica gel is 5%.

8. A multi-touch sensitive smart finger tip as claimed in claim 1, wherein the base and the clamping plates are both 3D printed and made of epoxy resin.

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