肌电信号的产生
表面肌电信号是由多个运动单元发放的动作电位序列,在皮肤表面呈现的时间和空间上综合叠加的结果
肌电信号特点
(1)sEMG是一维时间动作电位序列
(2)sEMG是交流信号,幅值一般和肌肉运 动力度成正比
(3)sEMG是一种非平稳的微电信号,其幅值在 0~1.5mv,有用信号频率位于 0~500HZ,主要能量集中在 20~150HZ
(4)SEMG一般比肢体运动超前 30~150ms产生,可以进行运动提前判断
(1)sEMG是微弱电信号,易受到心电信号和工频噪声的干扰,需要很高的共模抑制比,用模拟滤波器和双T陷波器将信号滤波放大到0~5V
(2)将电极、放大滤波电路、陷波电路封装在一起,加屏蔽层保护,降低传导耦合的干扰
(3)采集方式:探针式、电极片式
(4)已有sEMG采集系统:美国Delsys生产的Trigno、加拿大Thought生产的Myoscan
sEMG静态显示
clc
clear
addpath(genpath(pwd)); %% 将当前文件夹下的所有文件夹都包括进调用函数的目录
data=load('201801111534zhangaidong.mat');
ch1=data.data(:,1);
ch2=data.data(:,2);
% Hd=IIR_notchFilter(2000,50);
% ch1=filter(Hd,ch1); % 陷波后
% ch2=filter(Hd,ch2);
N=size(ch1,1);
figure(1);
plotHandlesEMG = zeros(2,1);
axesHandlesEMG = zeros(2,1);
for i = 1:2
axesHandlesEMG(i) = subplot(2,1,i);
plotHandlesEMG(i) = plot(axesHandlesEMG(i),0,'-y','LineWidth',1);
set(axesHandlesEMG(i),'XGrid','on','YGrid','on','XLimMode', 'manual','YLimMode', 'manual');
set(axesHandlesEMG(i),'Color',[.15 .15 .15],'XLim', [0 N],'YLim', [-.0005 .0005]);
title(sprintf('EMG %i', i));
end
set(plotHandlesEMG(1), 'Ydata', ch1);
set(plotHandlesEMG(2), 'Ydata', ch2);
sEMG动态显示
function dynamicShow_6ch
addpath(genpath(pwd)); %% 将当前文件夹下的所有文件夹都包括进调用函数的目录
load('20170927_xinhongyu.mat');
global plotHandlesEMG flag ch1 ch2 ch3 ch4 ch5 ch6;
ch1 = p3_open_ch1;
ch2 = p3_open_ch2;
ch3 = p3_grasp_ch1;
ch4 = p3_grasp_ch2;
ch5 = p3_snooze_ch1;
ch6 = p3_snooze_ch2;
flag=1;
t = timer('Period', 0.1, 'ExecutionMode', 'fixedSpacing', 'TimerFcn', {@updatePlots, plotHandlesEMG});
figure('CloseRequestFcn', {@localCloseFigure,t});
plotHandlesEMG = zeros(6,1);
axesHandlesEMG = zeros(6,1);
for i = 1:6
axesHandlesEMG(i) = subplot(3,2,i);
plotHandlesEMG(i) = plot(axesHandlesEMG(i),0,'b','LineWidth',1);
set(axesHandlesEMG(i),'XGrid','on','YGrid','on','XLimMode', 'manual','YLimMode', 'manual');
set(axesHandlesEMG(i),'XLim', [0 2000],'YLim', [-.00005 .00005]);
title(sprintf('EMG %i', i));
end
drawnow
start(t);
function updatePlots(obj, Event,tmp)
global plotHandlesEMG flag ch1 ch2 ch3 ch4 ch5 ch6;
data_ch1 = ch1(flag:flag+2000);
data_ch2 = ch2(flag:flag+2000);
data_ch3 = ch3(flag:flag+2000);
data_ch4 = ch4(flag:flag+2000);
data_ch5 = ch5(flag:flag+2000);
data_ch6 = ch6(flag:flag+2000);
flag=flag+200;
set(plotHandlesEMG(1), 'Ydata', data_ch1);
set(plotHandlesEMG(2), 'Ydata', data_ch2);
set(plotHandlesEMG(3), 'Ydata', data_ch3);
set(plotHandlesEMG(4), 'Ydata', data_ch4);
set(plotHandlesEMG(5), 'Ydata', data_ch5);
set(plotHandlesEMG(6), 'Ydata', data_ch6);
drawnow
function localCloseFigure(figureHandle,~,t)
stop(t);
delete(t);
delete(figureHandle);
经由肌电采集系统得到的原始肌电信号如图所示,肌电采集的频率为2000HZ,EMG1表示一秒内肌肉的动作电位序列,EMG2表示一秒内肌肉静息时的电位序列。由肌电采集系统得到的肌电信号虽然经过了硬件上的滤波、去噪等一系列的处理,但是仍然存在工频噪声、尖峰幅值等干扰,现在对得到的原始肌电信号进行软件滤波处理。
对原始肌电信号进行FFT变换,得到信号的单边振幅谱如图所示,可以看到50HZ的工频干扰很大,现在采用IIR数字陷波器,得到陷波后的信号单边振幅谱如图所示,消除工频干扰后,肌电信号的主要频率集中在0-500HZ,尤其是在10-300HZ。
由于肌电信号的主要频率集中在10-300HZ,现在对肌电信号进行软件数字滤波,常用的数字滤波器有巴特沃兹滤波器和切比雪夫滤波器。
- 巴特沃兹滤波器比切比雪夫滤波器具有更平滑的滤波特性
- 切比雪夫滤波器在过渡带的衰减更快,虽然频率响应的幅频特性没有巴特沃兹滤波器的好,但是与理想滤波器频率响应曲线之间的误差小。
为了保证特征的连续性,通常采用设置时间窗+增量窗的方式提取特征
时域特征
function feature = fARC(data)
% - ARC - Auto Regression Model Coefficients
order = 6;
f = real(lpc(data,order)'); %real()取复数的实数部分 lpc():Linear prediction filter coefficients
feature = -f(order+1,:); %首项默认为1,从第二项开始
end
function feature = fIAV(data)
% - IAV - Integrated Absolute Value
feature = sum(abs(data))/length(data);
end
function feature = fLogD(data)
feature = exp(mean(log(abs(data))));
end
function feature = fMAV(data)
% - MAV - Mean Absolute Value
feature = mean(abs(data));
end
function feature = fMAX(data)
feature = max(abs(data));
end
function feature = fNZM(data)
% - NZM - Non Zero Median 非0中位数
data_nonzero = data(find(data ~= 0));
feature = median(data_nonzero);
end
function feature = fRMS(data)
% - RMS - Root Mean Square
feature = sqrt(mean(data.^2));
end
function feature = fSSC(data)
% - SSC - Slope Sign Change, number times
DeadZone = 10e-7;
data_size = length(data);
feature = 0;
if data_size == 0
feature = 0;
else
for j=3:data_size
difference1 = data(j-1) - data(j-2);
difference2 = data(j-1) - data(j);
Sign = difference1 * difference2;
if Sign > 0
if abs(difference1)>DeadZone || abs(difference2)>DeadZone
feature = feature + 1;
end
end
end
feature = feature/data_size;
end
end
function feature = fVAR(data)
feature = var(data);
end
function feature = fWA(data)
% - WA - Willison Amplitude
Threshold = 10e-7;
data_size = length(data);
feature = 0;
if data_size == 0
feature = 0;
else
for i=2:data_size
difference = data(i) - data(i-1);
if abs(difference)>Threshold
feature = feature + 1;
end
end
feature = feature/data_size;
end
end
function feature = fWL(data)
% - WL - Waveform Length
feature = sum(abs(diff(data)))/length(data);
end
function feature = fZC(data)
% - ZC - Zero Crossing
DeadZone = 10e-7;
data_size = length(data);
feature = 0;
if data_size == 0
feature = 0;
else
for i=2:data_size
difference = data(i) - data(i-1);
multy = data(i) * data(i-1);
if abs(difference)>DeadZone && multy<0
feature = feature + 1;
end
end
feature = feature/data_size;
end
end
频域特征
function feature = fFMD(data)
% - MDF - Median Frequency
% 未陷波滤波
Fs = 2000;
feature = medfreq(data, Fs); % medfreq()计算中值频率,2015a版本才有
end
function feature = fFME(data)
% - MNF - Mean Frequency
%未陷波滤波
Fs = 2000;
feature = meanfreq(data, Fs);
end
function feature = fPSD(data)
% PSD Power Spectral Density 功率谱密度估计
[b,a]=butter(2,[0.01,0.5]);
x= filter(b,a,data);
Nfft = 512;
window = hanning(256);
noverlap = 128;
Fs = 2000;
[pxx,f]=pwelch(x,window,noverlap,Nfft,Fs);
feature = pxx; %得到的是一组数据257维
end
特征提取
clear
clc
addpath(genpath(pwd));
% 获取一维数据
load('mll.mat');
CH1 = double(mll_snooze_ch1);
CH2 = double(mll_snooze_ch2);
N = size(CH1,1);
%选择时间窗1秒(2000个点),增量窗0.1秒(200个点)
N = N/200;
for i=0:N-10
ch1 = CH1(200*i+1:200*i+2000,:);
ch2 = CH2(200*i+1:200*i+2000,:);
% 提取常规时域特征,每个通道11个特征,总共22个特征
A(1) = fIAV(ch1); B(1) = fIAV(ch2);
A(2) = fLogD(ch1); B(2) = fLogD(ch2);
A(3) = fMAV(ch1); B(3) = fMAV(ch2);
A(4) = fMAX(ch1); B(4) = fMAX(ch2);
A(5) = fNZM(ch1); B(5) = fNZM(ch2);
A(6) = fRMS(ch1); B(6) = fRMS(ch2);
A(7) = fSSC(ch1); B(7) = fSSC(ch2);
A(8) = fVAR(ch1); B(8) = fVAR(ch2);
A(9) = fWA(ch1); B(9) = fWA(ch2);
A(10)= fWL(ch1); B(10)= fWL(ch2);
A(11)= fZC(ch1); B(11)= fZC(ch2);
% 保存特征在TXT文件中
fid = fopen('features/timef/zzzzzz.txt','a');
for j=1:10
fprintf(fid,'%g\t',A(j));
fprintf(fid,'%g\t',B(j));
end
fprintf(fid,'%g\t',A(11));
fprintf(fid,'%g\n',B(11));
fclose(fid);
end
常用:LDA、KNN、SVM、ANN、MLP
康复系统、各个演示系统的分类模型均是ANN
网络结构:三层(输入层:通道数*特征数、隐含层、输出层:类别数)
完成的工作:
(1)偏瘫患者手部(张手、闭手、放松)三类识别
(2)正常人(12动作在线识别)6电极
(3)下肢6动作在线识别(6电极)
踝关节上拉、下勾;膝关节前伸、后拉;髋关节内收、外展