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CN113910270B - Soft joint bending angle sensor and rigid-flexible mixed hand sensing measurement method - Google Patents

Soft joint bending angle sensor and rigid-flexible mixed hand sensing measurement method Download PDF

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Publication number
CN113910270B
CN113910270B CN202111240489.6A CN202111240489A CN113910270B CN 113910270 B CN113910270 B CN 113910270B CN 202111240489 A CN202111240489 A CN 202111240489A CN 113910270 B CN113910270 B CN 113910270B
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joint
resistor
bending
input
sensor
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CN113910270A (en
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姜力
甄睿辰
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Harbin Institute of Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J13/00—Controls for manipulators
    • B25J13/08—Controls for manipulators by means of sensing devices, e.g. viewing or touching devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J15/00—Gripping heads and other end effectors
    • B25J15/0009—Gripping heads and other end effectors comprising multi-articulated fingers, e.g. resembling a human hand
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/30—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring angles or tapers; for testing the alignment of axes

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  • Engineering & Computer Science (AREA)
  • Robotics (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Human Computer Interaction (AREA)
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  • Force Measurement Appropriate To Specific Purposes (AREA)

Abstract

The invention provides a soft joint bending angle sensor and a rigid-flexible mixed hand sensing measurement method. And the resistance micro-variation signal is input into the single-ended ADC to collect signals through high input impedance after the sensitivity of the signal is improved through the bridge and the voltage difference of millivolt level at two ends of the bridge is amplified through high power, and the signals are transmitted to the main control through the SPI. The invention utilizes the feedback loop of the liquid metal sensor to feed back the current state to the upper computer in real time.

Description

Soft joint bending angle sensor and rigid-flexible mixed hand sensing measurement method
Technical Field
The invention belongs to the field of robot hands; in particular to a soft joint bending angle sensor and a method for measuring the sensing of a rigid-flexible mixed hand.
Background
Most of the existing robot smart hands are complex electromechanical systems composed of rigid components and kinematic pair joints. Due to its complex structure, these dexterous hands suffer from deficiencies in impact resistance, are complex to control and are expensive. There are certain disadvantages in some gripping or handling tasks for soft, easily deformable objects. How to detect the bending angle of the soft joint more sensitively and the detection degree is higher becomes a problem to be solved by the rigid-flexible mixed hand.
Unlike rigid hands, current soft hands generally lack sensors and lack body sensing functions. I.e. it is difficult to judge the motion of the finger in the absence of external sensor information. The position sensor used by the traditional robot lacks flexibility and cannot deform along with a soft hand or has a larger obstruction effect on deformation.
Disclosure of Invention
The invention provides a soft joint bending angle sensor and a rigid-flexible mixed hand sensing measurement method, which are used for enabling soft joint bending angle detection to be more sensitive and detection degree to be higher, and becoming a problem to be solved by the rigid-flexible mixed hand.
The invention is realized by the following technical scheme:
a soft joint bending angle sensor is characterized in that a resistance micro-change signal is used for improving signal sensitivity through an electric bridge, and after the voltage difference of millivolt levels at two ends of the electric bridge is amplified by high power, the voltage difference is input into a single-ended ADC (analog to digital converter) to collect signals with high input impedance, and the signals are transmitted to a main control through an SPI (serial peripheral interface);
the signal conditioning circuit of the sensor is a Kelvin bridge small resistance measuring circuit, the Kelvin bridge small resistance measuring circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a rheostat R7, a resistor RS, an amplifier AD, an ADC chip and an amplifier OP, the input voltage +5V is connected with one end of the resistor R1 and one end of the resistor R2, the other end of the resistor R1 is connected with one end of the resistor R3 and the positive input end of the amplifier AD, the other end of the resistor R1 is connected with one end of the resistor R3, one end of the resistor RS, one end of the resistor R5 and one end of the resistor R6, the other end of the resistor R3 is grounded after being connected with the other end of the resistor RS,
the other end of the resistor R5 is connected with the other end of the resistor R6 and the negative input end of the amplifier AD,
the No. 4 end of the amplifier AD is connected with the input voltage +5V and one end of the rheostat R7, the other end of the rheostat R7 is connected with the input voltage-5V and the No. 5 end of the amplifier AD, the Ref end of the amplifier AD and the output end of the amplifier OP are connected with the negative input end, and the positive input end of the amplifier OP is connected with the third end of the rheostat R7.
A rigid-flexible hybrid hand perception measurement method of a soft joint bending angle sensor, wherein the rigid-flexible hybrid hand perception measurement method comprises resistance measurement and finger contact force measurement;
the four-wire resistance measurement method in high-precision measurement is used for the resistance measurement, and the Kelvin bridge is used for improving the sensitivity of a measurement circuit;
the finger contact force measurement is due to the low rigidity and flexibility characteristics of the joints, and when a finger grips an object, the bending angle of the joints can be changed due to the force generated by the object and the finger; at the same input pressure, different contact forces and contact position distributions can lead to different bending angles; the input air pressure and the actual rotation angle of the joint of each air cavity reflect different contact force distribution of different contact positions of the finger and the object.
Further, the resistance measurement is specifically that the liquid metal sensor is connected into a Kelvin bridge through an FPC wire by a four-wire connection method, and the bridge resistance satisfies the relation: R1/r5=r3/R6. Let the magnification of the instrumentation amplifier be M AMP The bridge VCC is U i Then the circuit outputs U 0 The method comprises the following steps:
Figure BDA0003319048880000021
further, an AD8426 four-channel instrument amplifier is selected, and the amplification factor is 1000 times; selecting an + -5V isolated power supply for power supply; the corresponding output saturation voltage is +/-4.8V; each channel adjusts reference voltage through a potentiometer, matches impedance through an OP2177 voltage follower, and inputs a REF pin for zeroing; the power supply is provided with a capacitor to remove high-frequency clutter, and an output channel is added with low-pass filtering to directly drive a single-input ADC; the amplified voltage signal passes through a four-channel multiplexing ADC: ADS1220 converts to digital signals and communicates by isolating the SPI.
Further, the joint rotation angle measurement is specifically that the joint is regarded as the bending of uniform curvature when bending, and the bending angles of the IP joint and the MCP joint are respectively obtained by the following two formulas according to the resistance value measured by the circuit;
Figure BDA0003319048880000022
Figure BDA0003319048880000023
further, the finger contact force measurement is specifically that, due to the low rigidity and flexibility of the joint, when a finger grips an object, the bending angle of the joint is changed due to the force generated by the object and the finger; at the same input pressure, different contact forces and contact position distributions can lead to different bending angles; therefore, the input air pressure and the actual rotation angle of the joint of each air cavity reflect different contact force distribution of different contact positions of the finger and the object;
detecting the direction and the magnitude of the contact force of each phalange area when detecting the contact force of the finger; therefore, each finger needs to detect and output the pressure in the vertical direction at three positions, and a vector consisting of 3 force values in total; the input is a vector consisting of the input air pressure of 4 air cavities and 4 joint bending angles; therefore, a three-layer fully-connected neural network is adopted to fit the functional relationship;
when the network is trained, FSR is stuck to the phalangeal region of the finger to measure the contact force, the contact force data of different finger joint bending angles and air pressure input are measured to form a training set, and the obtained training set is used for training the network to obtain nonlinear approximation of the functional relation.
The beneficial effects of the invention are as follows:
the invention can simultaneously measure the bending angle and the contact force of the joint.
The invention has higher measuring precision of small resistance, and the theoretical measuring precision can reach 1 per mill.
The joint of the invention can realize large curvature bending in a small size and is close to the movement characteristic of the joint of a human hand. The sensor used in the invention can reduce the influence on the deformation of the soft joint.
Drawings
FIG. 1 is a schematic diagram of a drive perception integrated rigid-flex hybrid finger of the present invention.
Fig. 2 is a diagram of a kelvin bridge small resistance measurement circuit of the present invention.
Fig. 3 is a schematic view of the bending angle of the IP joint of the present invention.
Fig. 4 is a schematic view of the MCP joint bending angle of the present invention.
Fig. 5 is a schematic view of the contact force calculation of the present invention.
Fig. 6 is a schematic view of the contact force of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a method for integrating a multichannel flexible sensor into a rigid and flexible finger, which enables the finger to identify the bending angle and the contact force of the joint and provides a feedback signal for closed-loop control of the finger. Wherein, two IP joint sensors detect two IP joint bending angles respectively. MCP joints use symmetrical two-channel sensors, and bending and lateral swing angle information of the joints is obtained through signal decoupling. And obtaining contact force information through a trained multilayer network according to the relationship between air pressure and joint angle.
A rigid-flexible mixed finger comprising an IP interphalangeal joint 1, an MCP metacarpophalangeal joint 2, a DP phalange 3, an MP phalange 4, a PP phalange 5, a bending sensor 6 and a base 7; the IP interphalangeal joint 1 comprises a DIP interphalangeal joint 8 and a PIP interphalangeal joint 9;
the DP phalanges 3, the DIP interphalangeal joints 8, the MP phalanges 4, the PIP interphalangeal joints 9, the PP phalanges 5, the MCP metacarpophalangeal joints 2 and the base 7 are sequentially connected, and the bending sensor 6 is wound on the IP interphalangeal joints 1 and the MCP metacarpophalangeal joints 2;
the DP phalanges 3, the DIP interphalangeal joints 8, the MP phalanges 4, the PIP interphalangeal joints 9, the PP phalanges 5, the MCP metacarpophalangeal joints 2 and the bending sensor 6 are wrapped with a silica gel shell 9;
the DP phalanges 3, the DIP interphalangeal joints 8, the MP phalanges 4, the PIP interphalangeal joints 9 and the PP phalanges 5 form an air cavity which is of an inverted trapezoid structure in the length direction.
In the interphalangeal joint, the air cavity elastic matrix is made of Dragon skin 10 (Smooth-on, USA) liquid silica gel, and the cross section of the inner hole is in a cross section shape of a combination of semicircle and rectangle. The lower part of the air cavity with the cross section is provided with a strain limiting layer conveniently, the upper part of the air cavity is provided with a uniform semicircular surface so as to generate uniform expansion deformation, the middle part of the air cavity is provided with a rectangular structure for adjusting the ratio of the vertical height to the transverse width of the cross section of the air cavity, and compared with the pure semicircular cross section, the air cavity with the cross section of the air cavity can have larger cross section of the air cavity under the conditions of the same height and width.
In order to form unidirectional bending, a strain limiting layer (3M 8915) is applied to the lower part of the section of the air cavity, and glass fiber threads are wound in parallel outside the whole air cavity. When the air cavity is inflated, the strain limiting layer is considered to be bendable but not stretchable, so that deformation of the lower part of the air cavity is limited, and the upper part of the air cavity can still deform at a larger stretching proportion, so that the air cavity is deformed in a downward bending mode as a whole. The radial expansion of the air cavity is limited by integrally winding a layer of fiber yarn on the outer side of the air cavity, so that the inflation deformation of the upper part of the air cavity is further increased, and the high-pressure resistance capability of the air cavity is also increased, so that the air cavity can bear larger air pressure, output larger acting force and provide higher rigidity.
In order to realize bending with large curvature in a small range of the joint, the air cavity is designed into an inverted trapezoid structure in the length direction, and compared with a common structure, the structure can reduce the elongation ratio of the silica gel material at the upper part of the air cavity under the same joint bending angle, and remarkably reduce nonlinearity and material deformation resistance. Under the same inflation pressure, the inverted trapezoid air cavity can obtain a larger bending angle; the length of the non-tensile strained layer below the air cavity can be shortened at the same bending angle. This property helps to promote bending curvature at the joint and reduces the length-wise dimension of the joint. In order to realize the coupling bending of the joint between two fingers in a ratio of 1:1, the specific structure of the finger uses the same air cavity to connect two IP quasi-joints in a penetrating way, so as to realize the synchronous bending movement of DIP and PIP.
In metacarpophalangeal joints, the air cavity elastic matrix is also made of Dragon skin 10 (Smooth-on, USA) liquid silicone. Since the metacarpophalangeal joint needs to simultaneously realize bending motion in two directions, a joint air cavity arrangement scheme symmetrical relative to the center is used for simplifying the structure and modeling complexity. The joint section is two semi-elliptical arcs with the outer contour being up and down, and three circular air cavities are distributed on the section. In order to shorten the overall length of the bi-directional bending joint while increasing the bending curvature, each air chamber is wrapped with a fiber of double helical structure. The joint center is communicated with the interphalangeal joint air cavity by taking a glass fiber silicone tube as a central limiting air tube. The central limiting air pipe is used as a strain limiting layer of the metacarpophalangeal joint at the same time, the joint can be bent towards the opposite direction of the air cavities by inflating one air cavity, and the bending direction and the angle of the joint can be controlled to form coupled movement by controlling the inflation pressure of each air cavity so as to generate bending and side swinging at the same time.
A soft joint bending angle sensor is characterized in that a resistance micro-change signal is used for improving signal sensitivity through an electric bridge, and after the voltage difference of millivolt levels at two ends of the electric bridge is amplified by high power, the voltage difference is input into a single-ended ADC (analog to digital converter) to collect signals with high input impedance, and the signals are transmitted to a main control through an SPI (serial peripheral interface);
liquid metal was poured into capillary silicone tubing (0.3 mm inside diameter, 0.6mm outside diameter) over each joint, and the silicone tubing was inserted over the leads and connected to a Kelvin bridge. When the joint is bent, the silicone tube injected with liquid metal is lengthened to increase the resistance, and a tiny resistance signal is acquired through an electric bridge, and a 0-5V voltage signal is obtained through an amplifying circuit and AD conversion. Because the resistance of the liquid metal sensor is only 1-2 ohms, the contact resistance and the wire resistance have great influence on the measurement accuracy, and a Kelvin bridge is needed.
The signal conditioning circuit of the sensor is a Kelvin bridge small resistance measuring circuit, the Kelvin bridge small resistance measuring circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a rheostat R7, a resistor RS, an amplifier AD, an ADC chip and an amplifier OP, the input voltage +5V is connected with one end of the resistor R1 and one end of the resistor R2, the other end of the resistor R1 is connected with one end of the resistor R3 and the positive input end of the amplifier AD, the other end of the resistor R1 is connected with one end of the resistor R3, one end of the resistor RS, one end of the resistor R5 and one end of the resistor R6, the other end of the resistor R3 is grounded after being connected with the other end of the resistor RS,
the other end of the resistor R5 is connected with the other end of the resistor R6 and the negative input end of the amplifier AD,
the No. 4 end of the amplifier AD is connected with the input voltage +5V and one end of the rheostat R7, the other end of the rheostat R7 is connected with the input voltage-5V and the No. 5 end of the amplifier AD, the Ref end of the amplifier AD and the output end of the amplifier OP are connected with the negative input end, and the positive input end of the amplifier OP is connected with the third end of the rheostat R7.
A rigid-flexible hybrid hand perception measurement method of a soft joint bending angle sensor, wherein the rigid-flexible hybrid hand perception measurement method comprises resistance measurement and finger contact force measurement;
the four-wire resistance measurement method in high-precision measurement is used for the resistance measurement, and the Kelvin bridge is used for improving the sensitivity of a measurement circuit; coupling the contact resistance and the resistance error into a large resistance, so as to improve the measurement accuracy of the circuit;
the finger contact force measurement is due to the low rigidity and flexibility characteristics of the joints, and when a finger grips an object, the bending angle of the joints can be changed due to the force generated by the object and the finger; at the same input pressure, different contact forces and contact position distributions can lead to different bending angles; the input air pressure and the actual rotation angle of the joint of each air cavity reflect different contact force distribution of different contact positions of the finger and the object.
Further, the resistance measurement is specifically that the liquid metal sensor is connected into a Kelvin bridge through an FPC wire by a four-wire connection method, and the bridge resistance satisfies the relation: R1/r5=r3/R6. Let the magnification of the instrumentation amplifier be M AMP The bridge VCC is U i Then the circuit outputs U 0 The method comprises the following steps:
Figure BDA0003319048880000061
further, in order to reduce the volume of the system, an AD8426 four-channel instrument amplifier is selected, and the amplification factor is 1000 times; selecting an + -5V isolated power supply for power supply; the corresponding output saturation voltage is +/-4.8V; in order to eliminate steady-state offset errors of the instrument amplifier, each channel adjusts reference voltage through a potentiometer and matches impedance through an OP2177 voltage follower, a REF pin is input for zeroing, and influence of offset voltage is reduced; the power supply is provided with a capacitor to remove high-frequency clutter, and an output channel is added with low-pass filtering to directly drive a single-input ADC; the amplified voltage signal passes through a four-channel multiplexing ADC: ADS1220 converts to digital signals and communicates by isolating the SPI.
Further, the joint rotation angle measurement is specifically that the joint is regarded as the bending of uniform curvature when bending, and the bending angles of the IP joint and the MCP joint are respectively obtained by the following two formulas according to the resistance value measured by the circuit;
Figure BDA0003319048880000062
Figure BDA0003319048880000063
further, the finger contact force measurement is specifically that, due to the low rigidity and flexibility of the joint, when a finger grips an object, the bending angle of the joint is changed due to the force generated by the object and the finger; at the same input pressure, different contact forces and contact position distributions can lead to different bending angles; therefore, the input air pressure and the actual rotation angle of the joint of each air cavity reflect different contact force distribution of different contact positions of the finger and the object;
detecting the direction and the magnitude of the contact force of each phalange area when detecting the contact force of the finger; therefore, each finger needs to detect and output the pressure in the vertical direction at three positions, and a vector consisting of 3 force values in total; the input is a vector consisting of the input air pressure of 4 air cavities and 4 joint bending angles; therefore, a three-layer fully-connected neural network is adopted to fit the functional relationship;
when the network is trained, FSR is stuck to the phalangeal region of the finger to measure the contact force, the contact force data of different finger joint bending angles and air pressure input are measured to form a training set, and the obtained training set is used for training the network to obtain nonlinear approximation of the functional relation.
Fig. 5 and fig. 6 are diagrams of the method for measuring contact force based on the liquid metal sensor, wherein the standard fully-connected neural network used by the network and the counter-propagation algorithm used by the network are standard algorithms. A feature here is the use of such models for training and detecting force information of a rigid-flexible hybrid hand. Under the condition that a touch sensor is not used, taking the air pressure of the joint air cavity and the signals of the liquid metal sensor as inputs, and training to obtain an objective function f of output contact force:
F＝f(P,δ)
wherein F represents a contact force vector, P represents an air cavity air pressure input vector, and delta represents a joint rotation angle vector.

Claims (5)

1. The soft joint bending angle sensor is characterized by comprising an IP interphalangeal joint (1), an MCP metacarpophalangeal joint (2), a DP phalange (3), an MP phalange (4), a PP phalange (5), a bending sensor (6) and a base (7); the IP interphalangeal joint (1) comprises a DIP interphalangeal joint (8) and a PIP interphalangeal joint (9);
the DP phalanges (3), the DIP interphalangeal joints (8), the MP phalanges (4), the PIP interphalangeal joints (9), the PP phalanges (5), the MCP metacarpophalangeal joints (2) and the base (7) are sequentially connected, and the bending sensor (6) is wound on the IP interphalangeal joints (1) and the MCP metacarpophalangeal joints (2);
the DP phalanges (3), the DIP interphalangeal joints (8), the MP phalanges (4), the PIP interphalangeal joints (9), the PP phalanges (5), the MCP metacarpophalangeal joints (2) and the bending sensor (6) are wrapped with a silica gel shell;
the DP phalanges (3), the DIP interphalangeal joints (8), the MP phalanges (4), the PIP interphalangeal joints (9) and the PP phalanges (5) form an air cavity which is of an inverted trapezoid structure in the length direction;
liquid metal is injected into capillary silicone tubes above all joints, and two ends of each silicone tube are inserted into leads and connected to Kelvin bridges;
the resistance micro-variation signal is used for improving the signal sensitivity through an electric bridge, and after the voltage difference of millivolt level at two ends of the electric bridge is amplified by high power, the voltage difference is input into a single-ended ADC (analog to digital converter) to collect signals with high input impedance, and the signals are transmitted to a main control through an SPI (serial peripheral interface);
the signal conditioning circuit of the sensor is a Kelvin bridge small resistance measuring circuit, the Kelvin bridge small resistance measuring circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a rheostat R7, a resistor RS, an amplifier AD, an ADC chip and an amplifier OP, an input voltage +5V is connected with one end of the resistor R1 and one end of the resistor R2, the other end of the resistor R1 is connected with one end of the resistor R3 and the positive input end of the amplifier AD, the other end of the resistor R2 is connected with one end of the resistor RS, one end of the resistor R5 and one end of the resistor R6, the other end of the resistor R3 is grounded after being connected with the other end of the resistor RS,
the other end of the resistor R5 is connected with the other end of the resistor R6 and the negative input end of the amplifier AD,
the No. 4 end of the amplifier AD is connected with the input voltage +5V and one end of the rheostat R7, the other end of the rheostat R7 is connected with the input voltage-5V and the No. 5 end of the amplifier AD, the Ref end of the amplifier AD and the output end of the amplifier OP are connected with the negative input end, and the positive input end of the amplifier OP is connected with the third end of the rheostat R7.
2. The method for sensing measurement of a soft body joint bending angle sensor of a rigid-flexible hybrid hand according to claim 1, wherein the method for sensing measurement of a rigid-flexible hybrid hand comprises resistance measurement and finger contact force measurement;
the four-wire resistance measurement method in high-precision measurement is used for the resistance measurement, and the Kelvin bridge is used for improving the sensitivity of a measurement circuit;
the finger contact force measurement is specifically that the bending angle of the joint is changed due to the low rigidity and flexibility of the joint when the finger grips an object, and the force generated by the object and the finger; at the same input pressure, different contact forces and contact position distributions can lead to different bending angles; therefore, the input air pressure and the actual rotation angle of the joint of each air cavity reflect different contact force distribution of different contact positions of the finger and the object;
detecting the direction and the magnitude of the contact force of each phalange area when detecting the contact force of the finger; therefore, each finger needs to detect and output the pressure in the vertical direction at three positions, and a vector consisting of 3 force values in total; the input is a vector consisting of the input air pressure of 4 air cavities and 4 joint bending angles; therefore, a three-layer fully-connected neural network is adopted to fit the functional relationship;
when the network is trained, FSR is stuck to the phalangeal region of the finger to measure the contact force, the contact force data of different finger joint bending angles and air pressure input are measured to form a training set, and the obtained training set is used for training the network to obtain nonlinear approximation of the functional relation.
3. The method for sensing and measuring the rigid-flexible mixed hand of the soft joint bending angle sensor according to claim 2, wherein the resistance measurement is specifically that the liquid metal sensor is connected into a Kelvin bridge through an FPC wire by a four-wire connection method, and the bridge resistance satisfies the relation: r1/r5=r3/R6; let the magnification of the instrumentation amplifier be M AMP The bridge VCC is U i Then the circuit outputs U 0 The method comprises the following steps:
Figure QLYQS_1
4. a method for sensing and measuring a rigid-flexible mixed hand of a soft joint bending angle sensor according to claim 3, wherein an AD8426 four-channel instrument amplifier is selected, and the amplification factor is 1000 times; selecting an + -5V isolated power supply for power supply; the corresponding output saturation voltage is +/-4.8V; each channel adjusts reference voltage through a potentiometer, matches impedance through an OP2177 voltage follower, and inputs a REF pin for zeroing; the power supply is provided with a capacitor to remove high-frequency clutter, and an output channel is added with low-pass filtering to directly drive a single-input ADC; the amplified voltage signal passes through a four-channel multiplexing ADC: ADS1220 converts to digital signals and communicates by isolating the SPI.
5. The method for measuring the bending angle of the soft joint by using the rigid-flexible mixed hand according to claim 3, wherein the joint rotation angle measurement is specifically that the joint is regarded as bending with uniform curvature during bending, and the bending angles of the IP joint and the MCP joint are respectively obtained by the following two formulas according to the resistance value measured by the circuit;
Figure QLYQS_2
Figure QLYQS_3
wherein R is IP (beta) is the bending angle of the IP joint, l is the length of the strain limiting layer of the IP joint,
Figure QLYQS_4
the distance between the strain limiting layer of the IP joint and the sensor is beta, the bending plane angle of the IP joint is beta, the angle between the strain limiting layer of the IP joint and the sensor is theta, and s i Length of sensor for IP joint, R MCP (gamma) is the bending angle of MCP joint, < ->
Figure QLYQS_5
For the distance between the strain limiting layer of the MCP joint and the sensor, gamma is the bending plane angle of the MCP joint, sigma is the conductivity of the liquid metal, and d S The diameter of the inner cavity of the capillary silicone tube used for liquid metal is the serial number of the parallel part of the sensitive area of the liquid metal sensor, and t is the initial length of the MCP joint.
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