Fingertip pressure and position recognition sensor based on multi-color core flexible optical waveguideTechnical Field
The invention belongs to the technical field of sensors, and particularly relates to a pressure identification sensor, a pressure event detection method and a pressure event detection device.
Background
The touch sensor is a sensor for detecting pressure events by a piezoresistance principle, a capacitance principle, a piezoelectric principle, a quantum tunnel principle, a magnetic sensing principle or an optical principle, wherein the mechanical sensor realized based on the optical principle is widely applied due to the fact that the mechanical sensor is free from chemical inertia, free from electromagnetic interference, light in weight and the like.
In the related art, the mechanical sensor realized based on the optical principle comprises a waveguide inner core and a cladding. The pressure is detected by the loss of optical energy of the waveguide core when it is deformed by pressure. The light is bound in the waveguide core to propagate, and the pressure of the pressure event suffered by the waveguide core is determined according to the light intensity change degree.
However, when the pressure event is detected in the above manner, only the pressure value of the pressure event can be determined, and the amount of data detected by the mechanical sensor is limited.
Disclosure of Invention
In order to solve the problem that the stress direction detected by the existing mechanical sensor is uncertain, the invention provides a multi-color-core flexible optical waveguide-based multi-directional pressure recognition sensor for a robot fingertip.
The technical scheme adopted by the invention is as follows:
The fingertip pressure and position recognition sensor based on the multi-color-core flexible optical waveguide mainly comprises a waveguide inner core 2, an upper cladding 5 and a lower cladding 6, wherein the upper cladding 5 and the lower cladding 6 are wrapped outside the waveguide inner core 2;
The waveguide inner core 2 comprises three dyed waveguide inner cores 7, 8 and 9 with the same size and different colors, wherein the dyed waveguide inner cores 7, 8 and 9 are connected end to form a circular ring, the three dyed waveguide inner cores 7, 8 and 9 are respectively dyed into red, yellow and blue, the upper cladding 5 is wrapped at the upper part of the waveguide inner core 2, and the lower cladding 6 is wrapped at the lower part of the waveguide inner core 2, and the light refractive index of the waveguide inner core 2 is larger than the refractive indexes of the upper cladding 5 and the lower cladding 6;
The upper cladding 5 and the lower cladding 6 are provided with an entrance port 1 for being connected with a white light source, and an exit port 4 for being connected with a photoelectric receiver at a position opposite to the entrance port 1, wherein the photoelectric receiver is used for acquiring the spectrum of the outgoing light of the waveguide inner core 2, and the photoelectric receiver comprises 3 detection channels for respectively detecting red light, green light and blue light.
Preferably, the absorption wave bands of the three dyeing waveguide inner cores 7, 8 and 9 respectively correspond to 425nm, 550nm and 600nm so as to ensure that other wave bands except the absorption wave bands of the color band are not absorbed, and in addition, the transmittance of the three dyeing waveguide inner cores 7, 8 and 9 is 18% -21%;
preferably, the lower cladding layer 6 is made of a material having a relatively high hardness and being not easily deformed, so as to provide support for the bottom portion and prevent deformation of the lower cladding layer 6 from affecting the deformation amount in the waveguide core 2 and thus affecting the accuracy of the sensor.
Preferably, the light source of the entrance port 1 is a light emitting diode, and the photoelectric receiver of the exit end 4 is a micro spectrometer.
Further, the dye waveguide core contained in the waveguide core adjusts the detection range and sensitivity to pressure by adjusting the light absorption band and the light loss amount by changing the doping of pigment color.
The invention also provides a detection method of the pressure event based on the fingertip pressure and position recognition sensor, which comprises the following specific steps:
1) Under the condition that the light source is not turned on, acquiring the background light intensity Pa of the input sensor;
2) The method comprises the steps of turning on a light source, and acquiring emergent light intensity Py of a photoelectric receiver at an emergent end of a sensor in an initial state under the condition that the light source is not subjected to positive pressure;
3) Acquiring real-time emergent light intensity of a photoelectric receiver at an emergent end of a sensor, wherein the real-time emergent light intensity comprises light intensity of three channels of RGB, and the three channels detect light signals simultaneously;
4) The light transmittance T of the dyeing waveguide inner core corresponding to the detection channel of the photoelectric receiver is obtained through formula calculation according to the real-time emergent light intensity Ps, the emergent light intensity Py and the background light intensity Pa in the initial state;
;
Wherein, T represents light transmittance, Ps represents real-time emergent light intensity, Pa represents background light intensity of the photoelectric receiver and represents emergent light intensity in an initial state;
5) When the pressure is positive in one direction, the light of a single wave band is absorbed, the light intensity of the non-absorbed wave band shows the same change rule, and the equation of the light transmittance T changing along with the pressure p shows linear change, namely
;
Wherein, k and b can be obtained by a calibration mode, are the slope and intercept of a straight line respectively, and are obtained by back-pushing according to the equation:;
6) When the force direction of the vertical direction force and the force direction of each angle are changed, the force is obtained according to the force synthesis principle:
;
Wherein the vector isIs the relative response of any multi-directional pressure,Representing the pressures corresponding to the three channels,The current pressure magnitude and direction may be interpreted.
The invention also provides a device for detecting a pressure event, which comprises:
The photoelectric receiver comprises three channels of RGB, the output light emergent light intensity of the waveguide inner core is obtained, and the emergent light intensities corresponding to the three channels are obtained;
the determining module is used for determining the pressure p received by the dyeing waveguide inner core corresponding to each channel according to a linear equation of the incident light intensity and the emergent light strong light transmittance T along with the pressure p, and obtaining the triggering direction and the pressure value of the pressure event on the sensor according to the force synthesis principle.
The invention has the beneficial effects that:
the method has the advantages that the annular dyeing inner cores are arranged in the waveguide inner cores, light energy is input to the waveguide inner cores through the light sources, the light energy output by the waveguide inner cores 2 is received through the photoelectric receiver (micro spectrometer), so that the pressure event generated on the sensor is determined, the direction and the pressure generated on the sensor by the pressure event can be obtained by combining the input light energy according to the light energy output by the waveguide inner cores 2, the information quantity of data detected by the sensor is increased, and the detection efficiency of the pressure event is improved.
Drawings
FIG. 1 is a schematic illustration of the waveguide core and cladding of the tip pressure and position identification sensor of the present invention;
FIG. 2 is a transverse cross-sectional view of an optical waveguide in a fingertip pressure and position-recognition sensor provided by an exemplary embodiment of the invention;
FIG. 3 is a cladding view of an optical waveguide in a fingertip pressure and position-identifying sensor provided in an exemplary embodiment of the invention;
FIG. 4 is a graph of light absorption of three doped versus undoped dyes of the present invention;
FIG. 5 is a schematic view of three forward presses of the present invention;
FIG. 6 is a schematic diagram of a single direction press of the present invention except for the positive direction;
FIG. 7 is a schematic diagram of the present invention force applied in the OP direction for a finger tip pressure and position recognition sensor for an overall press;
FIG. 8 is a graph of the detected intensity of light for a press three positive directions with pressure applied RGB color gamut;
FIG. 9 is a graph of detected light intensity changes for an OP unidirectional press RGB color gamut plot of the present invention;
FIG. 10 is a graph of the detected intensity change of the RGB color gamut of the OP direction for an overall press with respect to a fingertip pressure and position recognition sensor of the present invention;
FIG. 11 is a schematic illustration of the present invention with a 1-fingertip pressure and position recognition sensor mounted to a mechanical hand simulator;
FIG. 12 is a schematic view of the present invention with a 2-finger tip pressure and position recognition sensor installed in a ball balancing system;
Fig. 13 is a flow chart of a method for detecting a pressure event according to an exemplary embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in further detail in the form of specific embodiments with reference to the accompanying drawings.
In the invention, the fingertip pressure and position recognition sensor consists of a waveguide inner core 2 and a cladding outside the waveguide inner core, wherein the refractive index of the inner core material is larger than that of the cladding, light can be restrained to propagate in the inner core, and when a pressure event is received on the sensor, the waveguide inner core is pressed to generate compression deformation, so that part of light energy propagated in the waveguide inner core is leaked and absorbed, and the light energy detected by the tail end of the waveguide inner core has light loss relative to the light energy of incident light, and the pressure value of the pressure event can be calculated according to the light loss. The light loss is characterized by the light transmittance T, which varies linearly with the equation of the magnitude of the pressure p for a given length of light propagation, i.eWherein k and b can be obtained by calibration, namely the slope and intercept of a straight line, and are obtained by back-pushing according to the equation:;
Referring to fig. 1, the fingertip pressure and position recognition sensor in this embodiment mainly includes a waveguide core 2, an upper cladding 5 and a lower cladding 6 wrapped around the waveguide core 2, and the refractive index of the waveguide core 2 is greater than that of the upper cladding 5 and the lower cladding 6, and light is totally reflected at interfaces of the waveguide core 2, the upper cladding 5 and the lower cladding 6, so that the light propagates in the waveguide core 2.
Fig. 2 is a transverse cross-sectional view of the optical waveguide in the tip pressure and position recognition sensor of the present embodiment, and the waveguide core 2 is intermediate the upper cladding 5 and the lower cladding 6 as shown in fig. 2.
Fig. 3 is a view showing the appearance of the finger tip pressure and position recognition sensor according to the present embodiment, and the finger tip pressure and position recognition sensor can be more clearly observed.
The waveguide core 2 comprises a first dyeing waveguide core 7, a second dyeing waveguide core 8 and a third dyeing waveguide core 9, wherein the first dyeing core 7 is dyed red, the second dyeing core 8 is dyed yellow, and the third dyeing core 9 is dyed blue. The three dyeing waveguide inner cores 7, 8 and 9 have the same size and are connected end to form a circular ring;
When white light passes through the dyeing waveguide inner cores of three colors to be changed into light of corresponding colors, when the white light passes through the blue dyeing waveguide inner core to be emitted, red light is absorbed, red light loss is larger when the blue dyeing waveguide inner core part is pressed, data corresponding to an R channel (red light channel) on the photoelectric receiver can be obviously changed, when the light transmittance T is used as a representation, an equation of the change along with the pressure p shows linear change, and similarly, the yellow dyeing waveguide inner core absorbs blue-violet light, and the blue dyeing waveguide inner core absorbs green light, and then the B channel (blue light channel) and the G channel (green light channel) on the photoelectric receiver respectively correspond to the same change rule.
In order to realize the waveguide manufacture, the following scheme is adopted in the embodiment:
The waveguide core 2 is polyurethane (Clear flex 30) with a first proportion, the polyurethane is a double-component rubber, the rubber proportion is that the proportion between the polyurethane (Clear flex 30) and a curing agent is 1:1 by volume, the waveguide core 2 comprises a first dyeing core 7, a second dyeing core 8 and a third dyeing core 9, the polyurethane (Clear flex 30) is adopted, the upper cladding 5 comprises PDMS, the PDMS proportion is that the proportion between a main agent and the curing agent is 10:1 by mass, and the lower cladding 6 comprises SEBS.
The light refractive index of polyurethane (Clear flex 30) is larger than that of PDMS and SEBS, the light refractive indexes of PDMS and SEBS are approximately equal, the flexibility of PDMS is higher than that of SEBS, and SEBS is harder and is not easy to deform, so that the sensor is suitable for being used as a bottom of a sensor.
The first dye core was polyurethane (Clear flex 30) of red pigment molecules (composed of 1mg of colorant and 1:1 ratio of 40mL of polyurethane (Clear flex 30)), the second dye core was polyurethane (Clear flex 30) of yellow pigment molecules (composed of 1mg of colorant and 1:1 ratio of 40mL of polyurethane (Clear flex 30), and the third dye core was polyurethane (Clearflex) of blue pigment molecules (composed of 1mg of colorant and 1:1 ratio of 40mL of polyurethane (Clear flex 30)), and the transmittance thereof was 18%, 19%, 21%, respectively, as shown in fig. 4.
The principle of the sensor for detecting a pressure event is described below with reference to fig. 4-9:
when the sensor is not subjected to positive pressure and is subjected to certain single positive direction pressure, only one wave band absorbs, the absorption wave band of the pigment in the positive direction changes linearly with the pressure value under the pressure of 0-15N, and three absorption wave bands are 425nm, 550nm and 600 nm. And conforms to the equation that the light transmittance T varies linearly with the magnitude of the pressure p:
;
Wherein k and b can be obtained by a calibration mode;
Firstly, under the condition that a light source is not turned on, acquiring the light intensity Pa of the background light (namely, ambient light) of an input sensor, and under the condition that the light source is not subjected to positive pressure, acquiring the emergent light intensity Py of an optical-electrical receiver at the emergent end of the sensor;
then, obtaining the incident light intensity of a sensor light source and the emergent light intensity of a photoelectric receiver at the emergent end of the sensor, wherein the emergent light intensity comprises the light intensities of three channels of RGB;
Calculating the light transmittance T of the dyeing waveguide inner core corresponding to the detection channel of the photoelectric receiver according to a formula respectively according to the real-time emergent light intensity Ps and the emergent light intensity Py in the initial state;
;
Wherein T represents light transmittance, Ps represents real-time emergent light intensity, Pa represents background light intensity of the photoelectric receiver, and Py represents emergent light intensity in an initial state;
Then, according to the linear equation of light transmittance T changing with pressure p, the pressure p received by the dyeing waveguide core represented by the corresponding channel is calculated, and the direction of the combined force is combined, so that three vectors can be usedRepresenting positive pressure experienced by the three dyed waveguide cores;
finally, according to the force synthesis principle, the positive pressure applied to the three dyed waveguide cores can be synthesized into one force, and the force is usedThe expression has the following rules:
;
Due to vectorsIs linearly independent, so the model is for three unknowns (blue, red, yellow forward)With unique solutions, thus obtainedThe current pressure magnitude and direction may be interpreted.
Thus, as shown in fig. 5, when a pressure event is received at the sensor, the pressure acts on the sensor, i.e. the pressure acts on the waveguide core 2, and the incident light generated by the light source propagates in the waveguide core 2, the photoelectric receiver is used to obtain the intensity of the light emitted from the waveguide core 2.
When the waveguide core 2 is not pressed, the incident light intensity of the waveguide core 2 in each absorption band is determined, and when the waveguide core 2 is pressed, the waveguide core 2 is subjected to compression deformation, and the emergent light intensity of the waveguide core 2 in each absorption band is determined. Thereby determining the pressure magnitude and pressure direction of the pressure event on the sensor according to the light transmittance calculation formula and the vector formula.
In summary, in the sensor provided in this embodiment, the first dye core, the second dye core and the third dye core are disposed in the waveguide core 2, the light energy is input to the waveguide core 2 through the light source, the optical energy output by the waveguide core 2 and the second dye core is received through the photoelectric receiver, so that the pressure event generated on the sensor is determined, and the pressure direction and the pressure magnitude generated on the sensor by the pressure event can be obtained by combining the input light energy according to the values of the optical energy output by the waveguide core 2 in different wavebands, so that the information amount of the data detected by the sensor is increased, and the detection efficiency of the pressure event is improved.
The application scene of the sensor related to the embodiment of the invention is explained, and the application scene of the sensor comprises the following scenes that the sensor is applied to an intelligent mechanical bionic hand scene and is arranged on finger fingertips of a bionic hand. For example, the pressure and the pressure direction of finger tips of the bionic hand when the bionic hand grabs the object are determined through the sensor, so that the current pressure required by the hand is accurately determined. So that the bionic hand is controlled more accurately when the object is gripped and the equipment is operated.
The ball balancing system is applied to a ball self-balancing system for making a pressure sensor, and can quickly sense the position of the ball when the ball is on a plane, so that the ball balancing system can acquire the information of the position of the ball more quickly, and the ball balancing system can be used for adjusting balance.
It should be noted that the above-mentioned embodiments are only for illustrating the present application and are not intended to limit the scope of the present application. Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the teachings of the present application, and such equivalents are intended to fall within the scope of the application as defined in the appended claims.