CN110946577A

CN110946577A - Flexible circuit board device for collecting arm electromyographic signals

Info

Publication number: CN110946577A
Application number: CN201911216695.6A
Authority: CN
Inventors: 王从庆; 谢作述
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2019-12-03
Filing date: 2019-12-03
Publication date: 2020-04-03

Abstract

The invention discloses a flexible circuit board device for collecting arm EMG signals, which can better fit the arm muscle group through the arbitrary bendability of FPC (Flexible Printed Circuit for short FPC), so that the arm EMG signal collection is more convenient and faster. The device is composed of a signal acquisition unit, a signal processing unit, a Bluetooth device and a power supply integrated on the FPC. Its characteristic is that the spring probe electrode can be evenly surrounded by the arm, and the spring probe can be in close contact with the arm muscles, which can better reduce the contact impedance, thereby increasing the signal-to-noise ratio of the spring probe electrode, and making the collected EMG The signal is more accurate; the present invention has the advantages of strong practicability and convenient use.

Description

Flexible circuit board device for collecting arm electromyographic signals

Technical Field

The invention relates to a flexible circuit board device for collecting arm electromyographic signals, which is used for recruitment of neuromuscular motion units and belongs to the field of rehabilitation robots.

Background

As more and more people have limb movement dysfunction, patients even lose self-care ability of life. The daily lives and works of these patients are seriously affected, and a great burden is imposed on the family as well as the society. The acquisition and decoding of the surface electromyogram signals are to extract the recruitment and release information of the neuromuscular unit and the MUPA (motor unit action potential) waveform information from the surface electromyogram signals, study the control mechanism of the neuromuscular system and lay an important foundation for the rehabilitation of neuromuscular diseases.

In the current traditional surface myoelectricity collecting electrode array system, most application scenes are collected by fixing electrodes on the surface of skin. If the array of the collecting electrodes can not be attached along with the fluctuation of the skin surface, motion artifacts are easily generated in the collecting process, which can interfere the quality of the collected electromyographic signals.

In order to collect the myoelectric signals of the arm of the patient more conveniently and rapidly, the signal collecting unit, the signal processing unit, the Bluetooth and the power supply are directly integrated on the FPC, so that the myoelectric signals can be more attached to the muscle group of the arm, and meanwhile, the signal collecting, processing and sending are integrated.

Disclosure of Invention

The invention aims to design a flexible circuit board device for collecting arm electromyographic signals, and solve the problem that a common electromyographic signal collecting device cannot be well attached to arm muscles.

The technical scheme is as follows: the technical scheme adopted by the invention is that the FPC device for acquiring the myoelectric signals of the arm comprises a signal acquisition unit, a signal processing unit, a signal transmitter and a power supply on the FPC. The plurality of paths of electromyographic signal acquisition units are longitudinally arranged on the FPC at intervals and are connected to the signal processing unit after being connected in parallel; the myoelectric signal acquisition unit acquires an electric signal generated by arm muscle movement, the signal processing unit performs analog-to-digital conversion on the acquired analog electric signal, and the signal transmitting device transmits the converted digital signal.

The signal acquisition unit has 16 paths, each path consists of two spring probe electrodes, an instrument amplifier and a resistance-capacitance element around the instrument amplifier, and the two spring probe electrodes are distributed on the FPC at equal intervals.

The instrumentation amplifier and the surrounding resistance-capacitance elements thereof are an AD620 chip and a capacitor and a resistor which are connected in series at the gain end of the instrumentation amplifier.

The signal processing unit is a filter circuit and an analog-to-digital converter which are integrated on the FPC.

The signal processing unit, the signal transmitter and the power supply are sequentially distributed at one end of the FPC device.

Drawings

FIG. 1 is a circuit diagram of one of the acquisition units;

FIG. 2 is a block diagram of a signal processing unit;

FIG. 3 is a circuit diagram of a band pass filter;

FIG. 4 is a reverse amplification circuit diagram;

FIG. 5 is a circuit diagram of an adder;

FIG. 6 is a general block diagram of the present invention;

fig. 7 is a diagram of a real object corresponding to the present embodiment.

Detailed Description

The invention discloses a Flexible circuit board (FPC for short) device for collecting arm myoelectric signals, which can be better attached to arm muscle groups through the arbitrary flexibility of the FPC and enables the collection of the arm myoelectric signals to be more convenient and faster. The device consists of a signal acquisition unit, a signal processing unit, a Bluetooth device and a power supply which are integrated on the FPC. The myoelectric muscle collecting device is characterized in that the spring probe electrode can uniformly surround the arm for a circle, the spring probe can be tightly contacted with arm muscles, contact impedance can be better reduced, and further the signal-to-noise ratio of the spring probe electrode is increased, so that the collected myoelectric signals are more accurate; the invention has the advantages of strong practicability, convenient use and the like.

The present invention is further illustrated by the following description in conjunction with the accompanying drawings and the specific embodiments, it is to be understood that these examples are given solely for the purpose of illustration and are not intended as a definition of the limits of the invention, since various equivalent modifications of the invention will become apparent to those skilled in the art upon reading the present specification, and all such modifications are intended to be included within the scope of the appended claims.

As shown in fig. 6, the arm electromyographic signal acquisition device comprises an FPC, and an electromyographic signal acquisition unit, a signal processing unit, a power supply and a signal transmitter provided thereon. The collecting device is wound on the arm for a circle, and then the collecting device is tightly attached to the arm through the elastic belt, and when the arm moves, the generated myoelectric signals sequentially pass through the collecting unit, the signal processing unit and the signal transmitter. The signal transmitter is preferably a bluetooth transmitter.

As shown in fig. 1, the circuit diagram of the internal circuit of a channel of the acquisition unit is shown, in which a pin 1 and a pin 4 of a chip are respectively connected with a spring probe electrode, so that differential amplification of an amplifier can be realized to eliminate common mode signals, capacitors and resistors connected in series between a pin 2 and a pin 3 of the chip are used to realize high-pass filtering of the signals, and grounded capacitors on a pin 5 and a pin 8

And

it acts as a decoupling capacitor.

After the metal electrode contacts with the skin surface, a trace amount of metal enters the electrolyte on the skin surface in the form of ions. In actual electromyographic signal detection, muscle swelling, skin shaking and the like are caused by the movement of the limb of a subject, the quantity of electrolytes in contact with the electrodes and the concentration of ions are changed, the charge distribution at the interface is disturbed, and the potential of the electrodes fluctuates along with the state of the movement of the limb of the person, and the fluctuation is called movement artifact.

The frequency spectrum of the motion artifact is mainly concentrated in a low frequency band below 10-20 Hz, the effective frequency of the electromyographic signal is above 20Hz, and the electromyographic signal are not overlapped, so the high-pass filtering is an effective method for eliminating the motion artifact. The invention adopts the technical scheme that a high-pass filter circuit is arranged in front of an instrument amplifier, so that the influence caused by motion artifacts can be avoided, as shown in figure 1, a capacitor and a resistor are connected in series at a gain adjusting end of the instrument amplifier to realize high-pass filtering, wherein R is_gAnd C_gThe amplifier is an instrument amplifier element and a high-pass filter element, and the gain of the amplifier is shown as the formula (1):

where A is the output gain, R₀49.4K Ω is the fixed resistance inside the instrumentation amplifier, R_gIs a resistance, C_gIs a capacitance, j is an imaginary unit, and w is a signal frequency;

the cutoff frequency of the amplifier is shown in equation (2):

wherein R is_gIs a resistance, C_gIs capacitance and F is cut-off frequency. The invention takes Rg as 800 omega and Cg as 10uF, the amplification factor of the direct current and the extremely low frequency motion artifact is 1, and the amplification factor of the electromyographic signal is 1+ R₀/R_gApproximately 62 times, and the cut-off frequency is 20Hz, effectively suppressing the motion artifact.

When a power supply supplies energy to each load, each load needs to work normally, on the premise that the supply voltage on the load needs to be stable, but devices in the load can dynamically absorb current when working, so that the supply voltage is extremely unstable, namely various high-frequency noises are superposed on the original voltage, and the noises can be regarded as alternating current noises caused by the working of the devices are coupled on direct current voltage. Thus, the ac-coupled dc supply voltage may affect not only the operation of the circuit in the load area, but also the operation of other loads connected to the same power source, which may cause problems in the operation of the circuits of those loads. Since each load will cause additional fluctuations in its power supply during operation, the fluctuations are locally minimized without affecting the operation of other loads. The way to reduce the effect of load supply fluctuations is to reinforce the feed that can respond instantaneously-smoothing out the shortfall in the rapid response of the main feed through the backup feed. The nature of the capacitor is energy storage, and the capacitor is used as standby electric energy to supply, so that fluctuation caused by instantaneous demand of the load can be smoothed, and the voltage of the load is ensured to be as stable as possible.

The invention removes the coupling effect by adding a 0.1uF patch capacitor on each power supply pin.

As shown in fig. 2, which is an internal structure diagram of the signal processing unit, the method includes performing 20-500Hz band-pass filtering on the collected 16 electromyographic signals, converting the signals into digital signals through an analog-to-digital converter, determining the sampling frequency of the analog-to-digital converter to be 1000Hz, and transmitting the data to bluetooth.

As shown in fig. 3, the circuit is a band-pass filter circuit diagram, the circuit is a butterworth circuit structure, a unity gain filter is adopted, a low-pass filter circuit and a high-pass filter circuit are connected in series to form band-pass filtering, and the power supply mode is 9V dual power supply. Wherein C is₁、C₂、C₃、C₄、R₁、R₂、R₃、R₄Is a parameter of the filter circuit. The former stage is high-pass filtering, and in order to implement high-pass filtering with cut-off frequency of 20Hz, the capacitor C used in the circuit₁＝C₂Calculate resistance R as 0.1uF₁、R₂The formula of (1) is:

where f is 20Hz, the cut-off frequency required for high-pass filtering, R can be calculated sequentially₁＝112KΩ，R₂56K Ω, R used in practice in the present invention₁＝100KΩ，R₂51K Ω, the resulting cut-off frequency is approximately 22 Hz.

In the latter stage, in order to realize low-pass filtering at 500Hz, the capacitor C in the circuit is taken₄＝2C₃When the resistance is 0.2uF, the resistance R is calculated₃、R₄The formula of (1) is:

wherein f is₁R can be calculated by taking 500Hz as the cut-off frequency required for low-pass filtering₃＝R₄2250 Ω, R used in practice in the present invention₁＝R₂The final cut-off frequency is obtained as 562Hz, 2K Ω.

As shown in fig. 4, which is a reverse amplification circuit diagram, V_in、V_outFor input and output, the electromyographic signals are processed for the second time after being connected in series with a band-pass filter circuitAmplifying, wherein the magnification formula is:

wherein R is_gThe resistor is a gain resistor, namely a resistor connecting the inverting input end of the operational amplifier and the ground. R_fThe feedback resistor is a resistor which is connected with the output end and the reverse input end of the operational amplifier. Get R_g＝1KΩ，R_f20K Ω, and the amplification factor n is-20, so that the final electromyographic signal is amplified by about 1200 times in total.

As shown in fig. 5, an adder circuit, V_in、V_outFor input and output, adopt V₁＝V₂The voltage range of the amplified electromyographic signal is maximally between-9V and 9V, the voltage is reduced to be between-1.5V and 1.5V by adopting a voltage division principle, and then V is added to the electromyographic signal by adopting an adder circuit₃Before the adder, two paths of signals to be superposed are respectively connected with a voltage follower, so that the signals are more stable, the voltage range of the electromyographic signals is changed into-3 v to 0v, and the formula of the adder is as follows:

wherein R is_f、R₁、R₂The resistors are all 10K omega, the voltage range of the obtained electromyographic signals is 0v to 3v, and the electromyographic signals can be used for AD sampling and analog-to-digital conversion.

Fig. 6 shows a general structural view of the present invention according to the above embodiment; fig. 7 shows a physical diagram corresponding to the present embodiment.

The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.

Claims

1. a collection device for arm myoelectric signal, is characterized in that, comprises the myoelectric signal collection unit, signal processing unit and signal transmission device that FPC is provided with on it, and the power supply end of FPC is also connected with power supply; The EMG signal acquisition units are arranged at intervals on the FPC, and are connected in parallel to the signal processing unit; the EMG signal acquisition unit collects electrical signals generated by arm muscle movement, and the signal processing unit performs analog-to-digital conversion on the collected analog electrical signals , the signal sending device sends the converted digital signal.

2. the acquisition device of arm myoelectric signal according to claim 1, is characterized in that, on described FPC, there are altogether 16 road myoelectric signal acquisition units, and each road myoelectric signal acquisition unit is all composed of two spring probe electrodes and An instrumentation amplifier and its surrounding RC components.

3. arm electromyographic signal acquisition device according to claim 2, is characterized in that, described 16 road electromyographic signal acquisition units are distributed on FPC at equal intervals, and the distance between two electrodes in each road acquisition unit is 2cm , arranged vertically on the FPC.

4 . The device for collecting arm EMG signals according to claim 2 , wherein the instrumentation amplifier is an AD620 chip. 5 .

5. The acquisition device of arm myoelectric signal according to claim 1, is characterized in that, described signal processing unit is a band-pass filter and analog-to-digital converter, is connected with described myoelectric signal acquisition unit, and the myoelectric The analog signal collected by the signal acquisition unit is filtered and then converted into a digital signal.

6 . The device for collecting arm EMG signals according to claim 1 , wherein the signal transmitting device is a Bluetooth device, which is connected to the analog-to-digital converter and is used to transmit the converted digital signal in real time. 7 .

7 . The device for collecting arm EMG signals according to claim 1 , wherein the power supply is an independent DC power supply, which is used to supply power to the acquisition unit, the signal processing unit and the signal transmitter. 8 .

8 . The device for collecting arm EMG signals according to claim 1 , wherein a 0.1uF chip capacitor is added to each power supply pin. 9 .