Tactile sensor and measuring circuit

Abstract

The present invention relates to the field of tactile sensors, and particularly relates to an inductive-array-type flexible tactile sensor using an RL oscillating circuit. The sensor comprises: a sensing layer, which is formed by means of a plurality of inductive units that are manufactured on a flexible PCB and arranged in M rows * N columns; an elastic layer, which is attached to the flexible PCB and made of materials that are neither electrically conductive nor magnetically permeable, such as PDMS or PI; and an induction layer, which is attached to the elastic layer and made of a material that is electrically conductive or magnetically permeable. The sensor has a sandwich structure; the elastic layer is located between the flexible PCB and the induction layer, and when subjected to a force, the adjacent elastic layer deforms, such that the relative position between the induction layer and the inductive sensing units of the sensing layer is changed, thereby changing the inductance of the corresponding inductive sensing units; and an RL oscillating circuit then converts the change in the inductance into a change in a pulse period, and by means of time-division scanning, a CPU control unit measures the inductance of each inductive sensing unit, converts same into a force magnitude, and outputs force measurement results to an external control system.

Description

Tactile sensor and measurement circuit TECHNICAL FIELD

[0001] The present application belongs to the technical field of sensor and humanoid robot, relates to a flexible inductive tactile sensor and measurement circuit, which is suitable for the fingers of humanoid robots, the soles of feet, electronic skins, clamping devices of industrial robots, medical and wearable devices, and the like, and the measurement circuit is also suitable for various force sensors, eddy current displacement sensors, eddy current flaw detectors, and the like. BACKGROUND

[0002] The array-type flexible tactile sensors of the prior art are mostly of the resistance type and the capacitance type, and have poor stability and poor anti-interference capability, and the inductive type of the prior art has been difficult to be productized due to large volume, the present application measures inductance by adopting a unique RL oscillation circuit, which can measure inductance of several tens of nanohenries, so that the diameter of the measured printed inductance can be reduced to below 2 mm, thereby realizing a flexible array inductive tactile sensor, the measurement unit corresponding to one inductor can also realize 3D force measurement by selectively combining 4 inductance measurement units arranged in a rectangular array, and the array-type flexible tactile sensor can measure both normal force and 3D force by selectively allowing most of the units to measure normal force and a small number of selected positions to measure 3D force. SUMMARY

[0003] The present application is realized by the following technical solutions

[0004] The sensor layer is composed of M rows and N columns of spiral inductance coils made on a flexible PCB board, the elastic layer is attached to the sensor layer of the flexible PCB board, and the inductor layer is attached to the elastic layer, the elastic layer is located between the sensor layer and the inductor layer, and is a sandwich structure, the row analog switch circuit and the column analog switch circuit for selecting the measured inductance unit are composed of analog switch chips or NMO S transistors with low internal resistance, and the on-off of the switch is controlled by the CPU, and the RL oscillation circuit for measuring inductance and the measurement control CPU are composed.

[0005] The RL oscillation circuit is connected in series with the measured inductance through a current sampling resistor, only one row switch element and one column switch element are turned on at the same time, and an inductance unit at the intersection of the row switch and the column switch is measured. The RL oscillation circuit has a lower threshold voltage and an upper threshold voltage, a voltage comparator, and a charging and discharging circuit controlled by the voltage comparator. The charging circuit is a resistor voltage dividing circuit or a voltage source, and the discharging circuit is an NMOS transistor controlled by the voltage comparator. When the voltage drop on the current sampling resistor is less than the lower threshold voltage, the charging process starts, and the charging circuit increases the current flowing through the measured inductance. When the voltage drop on the current sampling resistor is greater than the upper threshold voltage, the charging process ends, and the discharging circuit starts to work, starting the discharging process, and the current flowing through the measured inductance starts to decrease. When the voltage drop on the current sampling resistor is less than the lower threshold voltage, the discharging process ends, and the charging process starts again. The above process is repeated to generate a pulse signal with a pulse period proportional to the measured inductance. When the voltage drop on the current sampling resistor is between the lower threshold voltage and the upper threshold voltage, the charging process or the discharging process remains in the current state.

[0006] The elastic layer attached to the flexible PCB board is a columnar array or a tubular array or a sheet.

[0007] The sensing layer attached to the elastic layer is a circular disc array or a polyhedral array or a sheet, and the axis of each circular disc in the circular disc array is aligned with the axis of the spiral inductance coil on the inductance array on the flexible PCB board.

[0008] The sensing layer circular disc array is attached to the elastic layer, and the axis of each circular disc is aligned with the intersection of the diagonals of a unit composed of every 4 rectangularly arranged inductances, so that normal force and tangential force can be measured, and the sensing layer can also be other polygonal metal sheets.

[0009] The inductance array made on the flexible PCB board is a single-layer or multi-layer spiral inductance coil made by PCB process, and the inductance coil can be circular, elliptical, rectangular, or other polygonal.

[0010] The elastic layer is made of non-conductive and non-magnetic materials such as PDMS and PI rubber plastics and composite materials, and the normal and tangential elastic coefficients of the elastic layer are changed by selecting the material of the elastic layer and processing it into various columnar, spherical, and conical microstructures, thereby changing the measurement force range.

[0011] The induction layer is a sheet made of soft magnetic rubber sheet or a round sheet or other polygonal metal sheet made of copper foil, etc. When the induction body is a soft magnetic material, the magnetic resistance of the magnetic circuit of the inductor will change. When the induction layer is a conductor, the changing magnetic field in the inductor will generate eddy current in the induction layer, which will change the inductance of the inductor.

[0012] The induction layer can also be a metal support structure of the robot body, and the flexible layer is attached to the metal support surface, and the flexible PCB board of the sensing layer is attached to the flexible layer. Specific embodiments

[0013] The implementation of the present application can be realized by the following two examples BRIEF DESCRIPTION OF DRAWINGS

[0014] Fig. 1 is a schematic structural diagram of an array tactile sensor according to an embodiment of the present application

[0015] Fig. 2 is a schematic structural diagram according to another embodiment of the present application

[0016] Fig. 3 is a schematic structural diagram of a 3D measurement unit capable of measuring normal force and tangential force according to the embodiment of the present application

[0017] Fig. 4 is a circuit principle of a flexible inductive tactile sensor and a measurement circuit according to the present application

[0018] In Figs. 1-3, 1 is a sensing layer, 2 is a flexible layer, 3 is an induction layer, L1, L2, L3, L4 are spiral inductance coils made on the sensing layer

[0019] In Fig. 4, U1A is a voltage comparator, U2 is a single-chip microcomputer, U3A is a voltage follower, R1-R5 are resistors, C1 is a filter capacitor, DW is a parallel voltage stabilizing circuit, T1-TM are row analog switches, P1-PM are row analog switches for voltage, Q1 is an NMOS transistor, K1-KN are column analog switches, L11-LMN are spiral inductance coils made on the flexible PCB board.

[0020] The working principle of the embodiment 1 is as follows

[0021] Referring to Fig. 1

[0022] The sensing layer is composed of spiral single-layer or multi-layer inductance coils printed on the flexible PCB.

[0023] The flexible layer is composed of elastic materials such as PDMS silicone rubber, engineering plastics, composite materials, etc. which are not magnetic and not conductive. By adjusting the composition of the elastic material or adding bubbles or processing various micro shapes, the elastic coefficient of the flexible layer can be adjusted.

[0024] The inductive layer is a soft magnetic material capable of changing the magnetic reluctance of the inductive coil, or a metal sheet capable of generating an electric eddy current in the inductive coil.

[0025] When the tactile sensor is installed on a metal surface, such as a finger of a humanoid robot, a sole, an external metal surface of a body, etc., the metal surface can be directly used as the inductive layer, and one surface of the elastic layer is directly attached to the metal surface, and the sensing layer is attached to the elastic layer.

[0026] When the sensing layer and the inductive layer are subjected to a pressure, the elastic layer sandwiched therebetween is deformed, so that the relative positions of the sensing layer and the inductive layer are changed, thereby causing a change in the inductance of the corresponding inductive coil. The RL oscillation circuit converts the change in the inductance into a change in the pulse period. The CPU and the switch array measure the change in the pulse period caused by the change in the inductance of each point by time division, thereby calculating the elastic deformation of the elastic layer, and according to the elastic system of the elastic layer, the force value of each inductive coil position is calculated and transmitted to the upper control system.

[0027] The working principle of Example 2 is as follows

[0028] Referring to FIG. 2, in Example 2, there are both a unit for measuring a normal force and a unit for measuring a 3-dimensional force. Each unit for measuring a normal force is composed of a spiral inductive coil, an elastic layer attached to the surface thereof, and an inductive layer. Each unit for measuring a 3-dimensional force is composed of four spiral inductive coils, an elastic layer attached to the surface thereof, and an inductive layer.

[0029] The principle of measuring a 3-dimensional force is described with reference to FIG. 3.

[0030] The metal sheet of the inductive layer only partially covers the surface of the corresponding sensing layer spiral inductive coil, so that when the inductive layer and the sensing layer are subjected to a normal force (Z direction), the distance between the inductive layer and the sensing layer spiral inductive coil is changed.

[0031] When the inductive layer and the sensing layer are subjected to a tangential force (X or Y direction), the tangential position between the inductive layer and the sensing layer spiral inductive coil is changed, that is, the coverage area is changed, and both changes cause a change in the inductance of the inductive coil.

[0032] In FIG. 3, when the inductive layer is subjected to a normal force (Z direction), the distance between the inductive layer and the inductive coil is simultaneously changed, and the inductance of L1, L2, L3, and L4 is simultaneously increased or decreased, that is, Fz=L1+L2+L3+L4

[0033] When the sensing layer is subjected to a tangential force in the X direction, the overlapping area between the sensing layer and the inductance coils L1 and L3 decreases, the overlapping area between the sensing layer and the inductance coils L2 and L4 increases, the inductance of L1 and L3 increases, the inductance of L2 and L4 decreases, and Fx=L1+L3-L2-L4.

[0034] When the sensing layer is subjected to a tangential force in the Y direction, the overlapping area between the sensing layer and the inductance coils L2 and L4 decreases, the overlapping area between the sensing layer and the inductance coils L1 and L3 increases, the inductance of L2 and L4 increases, the inductance of L1 and L3 decreases, and Fy=L2+L4-L1-L3.

[0035] According to the change of the inductance, the relative position of the sensing layer and the inductance coils in the XYZ direction can be calculated, and according to the elastic system of the elastic layer in the XYZ direction, the 3D force acting on each inductance coil can be calculated and transmitted to the upper control system.

[0036] The circuit principle of the above two embodiments of the present application is shown in Fig. 4.

[0037] The working process of the circuit is as follows: for example, if the inductance of the inductance coil at the second row and the second column is to be measured, the CPU sends a command to turn on the analog switch T2 of the second row and turn off the analog switches T1 to TM of the other rows, so that the second row is selected. Meanwhile, the analog switch K2 of the second column is turned on and the analog switches K1 to KM of the other columns are turned off, so that the second column is selected, that is, the inductance coil L22 at the intersection of the second row and the second column is selected.

[0038] When the voltage drop VPPI of the current flowing through the inductance coil L22 on the resistor R1 is less than VT, the output of the comparator is low, and Q1 is turned off. The voltage value of VPPO is the voltage value of the parallel voltage stabilizing circuit. Since this voltage is designed to be greater than VPPI, the voltage VT is the upper threshold voltage at this time, and the current in the inductance coil L22 begins to increase.

[0039] When the current in the inductance coil L22 increases to a voltage drop VPPI on R1 greater than VT, the output of the voltage comparator is high, and Q1 is turned on. At this time, VPPO becomes 0 voltage, and the voltage VT becomes the lower threshold voltage. It is noted that the lower threshold voltage < the upper threshold voltage < the VPPO voltage when Q1 is turned off, and the current in the inductance begins to decrease, but the direction of the current does not change.

[0040] When the current decreases to a voltage drop VPPI on R1 less than the lower threshold voltage, the output of the voltage comparator becomes low again, Q1 is turned off, VPPO becomes a voltage, and the voltage VT becomes the upper threshold voltage. The current in the inductance begins to increase again.

[0041] When the voltage drop VPP1 on R1 is between the lower threshold voltage and the upper threshold voltage, the output state of the voltage comparator does not change, so a pulse signal with a pulse period proportional to the inductance of the inductor L22 is generated at the output end PP of the voltage comparator.

[0042] The voltage follower U3A and the row analog switch P1~PM for equal voltage form an anti-crosstalk circuit. When a certain row is selected by the row analog switch, the non-selected rows are connected to the output end of the voltage follower U3A through the row analog switch for equal voltage, so that the two ends of the inductors in the selected column except the measured inductor are at the same potential, and the current in the inductor is zero, which is equivalent to being disconnected.

[0043] Since the inductance array of the sensing layer has M rows and N columns, there is crosstalk between the inductors during the measurement process in the row-column scanning mode. When a measured inductor in a certain row and column is selected, other inductors will also form a loop through other row and column wires to affect the measurement result. When the number of inductors in the sensing layer is not large, it is recommended to use one inductor corresponding to one analog switch, that is, the circuit in FIG. 4 is arranged in a row, and only the column analog switch is used to select the inductor, and the row analog switch, the row analog switch for equal voltage, and the voltage follower are cancelled. In this way, the crosstalk between the inductors is avoided.

[0044] The CPU of the control circuit periodically selects and measures the inductance of each spiral inductor coil of the sensing layer in a time-division manner, so as to calculate the force value at the position of each spiral inductor coil. The CPU calibrates, corrects, and linearizes the force value at the position of each inductor coil.

[0045] Since the above circuit is the current rise and fall process of a one-value RL circuit, the oscillation period of the RL oscillation circuit can be calculated by the three-element method. When the inductance array is relatively large, the inductance array can be divided into several groups and measured by the respective analog switch array and the RL oscillation circuit. The measurement unit composed of 3 inductor coils arranged in a triangle shape can also measure 3-dimensional force.

Claims

1. A tactile sensor and measuring circuit, characterized by, The sensor layer includes an array sensor unit made of spiral inductance coils on a flexible PCB board, an elastic layer attached to the sensor layer of the flexible PCB board, and a sensing layer attached to the elastic layer, with the elastic layer between the sensor layer and the sensing layer. The array sensor unit is selected by an analog switch circuit, the inductance is measured by an RL oscillation circuit, and a measurement and control CPU is provided.

2. The flexible inductive tactile sensor and measurement circuit according to claim 1, characterized in that The RL oscillation circuit is connected in series with the measured inductance through an analog switch circuit and a current sampling resistor. The RL oscillation circuit has a lower threshold voltage and an upper threshold voltage, a voltage comparator, and a charging and discharging circuit controlled by the voltage comparator.

3. The flexible inductive tactile sensor and measurement circuit according to claim 1, characterized in that, The elastic layer attached to the flexible PCB board is made of non-conductive and non-magnetic elastic materials such as PDMS and PI engineering plastics and composite materials.

4. The flexible inductive tactile sensor and measurement circuit according to claim 1, characterized in that The inductance array on the flexible PCB board is made of single-layer or multi-layer spiral inductance coils using PCB technology.

5. The flexible inductive tactile sensor and measurement circuit of claim 1, wherein, The sensing layer is made of soft magnetic rubber sheets or conductive materials such as copper foil.

6. The flexible inductive tactile sensor and measurement circuit according to claim 5, characterized in that The sensing layer is the metal support structure of the robot body, the elastic layer is attached to the metal support surface, and the flexible PCB board of the sensor layer is attached to the elastic layer.

Images