Real-Time Measurement of Prehensile EMG signals Master Thesis Saksit Siriprayoonsak Supervisor: Marko Vuskovic Department of Computer Science San Diego State University August 24, 2005 Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak Contents Introduction EMG Overview Apparatus for EMG Measurement Implementation of EMG Capture Program Experimental Results Conclusion Copyright 2005 by Saksit Siriprayoonsak

Multifunctional Prosthetic Hand Control A research in Robotics Laboratory, SDSU Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak Object of Thesis Main purpose: Design and develop hardware and software for measuring surface EMG signals from real human muscles in real-time. Immediate application: To control the existing SDSU multifingered robot hand. Hardware-brings the develop of EMG Amplifier Software-brings the develop of EMG Capture Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak EMG Overview EMG – Electromyography Electromyography measures the electrical impulses of muscles at rest and during contraction. Amplitudes of EMG signal range between 0 to 10 mV (peak-to-peak) or 0 to 1.5 mV (rms). Frequency of EMG signal is between 0 to 500 Hz. The usable energy of EMG signal is dominant between 50-150 Hz. Source: http://www.delsys.com/library/papers/SEMGintro.pdf Copyright 2005 by Saksit Siriprayoonsak

Amplification of EMG Signals Factors to be considered: Boost signal to TTL standard level (± 5 V.) Enough gain Noise/Artifact problem Filter, stability of electrodes attached to skin, proper grounding DC offset or bias problem Bias adjustment Power consumption Consume less current -Enough Gain Copyright 2005 by Saksit Siriprayoonsak

EMG Measurement Stages Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Electrode and Extension Stereo phone wire with 3 conductors Positive input to preamplifier Negative input to preamplifier Shield as the input of body reference circuit Velcro strap for securing the electrode to the skin Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Electrode and Extension (cont.) Plastic piece and snap on for holding electrode elements Dimension of 1 inch between electrode contacts 4 electrode extensions and 1 body reference extension Total of 9 electrode contacts Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Power Supply Dual Supply Positive Power Supply Negative Power Supply Two 9-volt batteries connected in series Capacitors provide stability of electrical current. Power Supply Unit Circuit Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Preamplifier Industry standard instrumentation amplifier op-amp (INA2128) Accuracy: providing high bandwidth at high gain and output offset current Differential amplifier circuit with 2 inputs High gain to boost the EMG signals Body Reference Circuit or Feed Back (OPA2604) Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Preamplifier (cont.) BURR-BROWN INA2128 Application Information Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Preamplifier (cont.) Preamplifier with Body Reference Circuit (1 channel) Gain Equation: Find RG at Gain = 1,000: Find Gain at RG = 22 ohm: Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Averaging Body Reference Circuit Common body reference circuit for 4 channels Using summing amplifier circuit and sign changing circuit Sign Changing Circuit (Inverting Amplifier Circuit) Inverting Summing Amplifier Circuit For independent R1, R2, R3, and R4: For independent R1, and R2: For R1= R2= R3= R4: For R1= R2: Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Average Body Reference Circuit (Cont.) Common Body Reference Output: Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak EMG Amplifier: Filter Suppress noise that has been amplified by the preamplifier Help to sink any DC current that cause bias to the output Select particular signal frequency range Use RC High Pass Filter of 12 Hz Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Filter (cont.) RC High Pass Filter Cutoff Frequency of 12Hz RC High Pass Filter Cutoff Frequency: Cutoff Frequency of 12 Hz: Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Amplifier and Bias Adjustment Provide abilities to amplify and adjust reference level of output signals Individual amplifier and bias adjustment unit for each channel Use Non-Inverting circuit for amplifier unit Use Voltage Follower Offset Adjustment circuit for bias adjustment unit Provide Gain of 21 times Provide Offset of ± 9 volts Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Amplifier and Bias Adjustment (cont.) Non-Inverting Amplifier Circuit Non-Inverting Output: Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Amplifier and Bias Adjustment (cont.) Amplifier Circuit with Gain Adjustment Amplifier Gain: At : At : Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Amplifier and Bias Adjustment (cont.) Case 1: at 0% of : ( ohms; volts ) Offset Adjustment for Voltage Follower Case 2: at 50% of : ( ohms; volts ) Output of the circuit: Case 3: at 100% of : ( ohms; volts ) Copyright 2005 by Saksit Siriprayoonsak

EMG Amplifier: Amplifier and Bias Adjustment (cont.) Case 1: at 0% of : ( ohms; volts ) Bias Adjustment Circuit Case 2: at 50% of : ( ohms; volts ) Output of the circuit: Case 3: at 100% of : ( ohms; volts ) Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak A/D Interface Card NI 6220 M-Series Multifunction DAQ Clock Speed: 8 Hz, up to 1 MHz Analog Input Resolution: 16 bits Number of Analog Input Channels: 8 Copyright 2005 by Saksit Siriprayoonsak

Final Product Assembly Netlist, Circuit designed and tested on breadboard Schematic created by Multisim8 PCB layout created by Ultiborad7 Copyright 2005 by Saksit Siriprayoonsak

Final Product Assembly (cont.) A schematic diagram is drawn using Multisim8. Netlist contains all circuit connections. Netlist is transferred to Ultiboard7 for PCB layout. PCB is a double layer (top copper layer and bottom copper layer) Through holes connect between 2 layers. Netlist is database. Copyright 2005 by Saksit Siriprayoonsak

Final Product Assembly (cont.) PCB shipped by the manufacturer Placing the battery on the side, weight balance Copyright 2005 by Saksit Siriprayoonsak

Final Product Assembly (cont.) PCB after soldering Copyright 2005 by Saksit Siriprayoonsak

Calibration Procedure Each channel is individually calibrated. Input is equal to output (100 mV.) If an arbitrary gain is needed, the output is desired gain value multiplied by input. Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak EMG Capture Provides 3 play modes: Real-Time, Record, and Playback mode. Able to save and open EMG data to/from file. Display features: Voltage scales Time scales Readout of exact values Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: User Interface Left side for control. Right side for adjust display Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Main Parameter Subpanel Working with Real-Time mode and Record mode. Maximum Buffer Size (Samples per Channel) Sampling Rate (Hz) Buffer size has unit in sampler/channel. Sampling Rate has unit in Hz. Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak EMG Capture: Play Mode Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Real-Time Mode START Start real time mode Stop real time mode Freeze output display for examine interesting segments or save the data Resume real time mode Save data in buffer to file STOP Pause Resume Save Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Record Mode Start to Record the signals in specific time range in seconds. Save the data to file START Save Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Playback Mode - Open EMG data file (.emg) Open Standard window open dialog Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Voltage Scale Voltage scale is independent for each channel. Alternative voltage scales: 200 mV/Div. 500 mV/Div. 1 V/Div. 2.5 V/Div. 5 V/Div. Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Time Scale All channels use the same time scale Alternative time scales: 1 mSec/Div. 5 mSec/Div. 10 mSec/Div. 50 mSec/Div. 100 mSec/Div. 200 mSec/Div. 400 mSec/Div. Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Time Slider Scroll time slider to view data from beginning to the end. The numbers on the left and right corner correspond to the time stamp of the first and the last sample shown on the output display screen. ‘5.416’ is 5 seconds and 416 milliseconds. Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak EMG Capture: Readout Read extract value at pink vertical line Need not to compute the value of scale Unit: Time (sec) , Voltage (V) Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Output Display Displays 4 channels Voltage: 4 divisions 2 positive divisions 2 negative divisions Time: 15 divisions Maximum Display: ±10 volts with 5 volts/Div. 6 seconds with 400 mSec/Div Copyright 2005 by Saksit Siriprayoonsak

EMG Capture: Status Bar Guide user through the usage Display important message eg. Number of samples that went into the buffer. Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak EMGC Implementation Developed by using Microsoft Visual C++ tool GUI developed with MFC (Microsoft Foundation Class) library Runs on Windows 2000 machine which has A/D interface card installed A/D Interface Card: Multifunction Data Acquisition (DAQ), M-6220 series from National Instrument Company Copyright 2005 by Saksit Siriprayoonsak

EMGC Implementation: Output Buffer Structure struct SOutputData { int output_ii; //Iteration start from 0 double time; //Time stamp in Second double volt1; //Voltage value for CH1, CH2, CH3, and CH4 double volt2; double volt1; }; CArray <SOutputData, SOutputData> dumpDataArray; CArray class from MFC Library used to store input signal data. CArray can dynamically shrink and grow if necessary. Copyright 2005 by Saksit Siriprayoonsak

EMGC Implementation: Creating Voltages and Time Scales //For Calculation double voltScaleSet[5] = {5.0, 2.5, 1.0, 0.5, 0.2}; //unit in volt/div //For Screen Display CString voltScaleStrMap[5] = {“5 Volt/Div”, “2.5 Volt/Div”, “1 Volt/Div”, “500 mVolt/Div”, “200 mVolt/Div”}; Use spin control to select the scales. Spin control increase/decrease spin value by a specific number of steps. Use spin value as the index of scale array. Copyright 2005 by Saksit Siriprayoonsak

EMGC Implementation: Draw Grid for Graph Output Use CDC class (Class Device-Context object) to draw output on the screen. The CDC class is a class from the MFC library. CDC provides various kinds of drawing functions (working with drawing tool, converting the coordinates, drawing rectangles, drawing circles, drawing text, changing the color) CDC provides various kinds of drawing functions such as working with drawing tool, converting the coordinate, drawing rectangle, drawing circle, drawing text, or changing the color. Copyright 2005 by Saksit Siriprayoonsak

EMGC Implementation: Draw Grid for Graph Output (cont.) private: //Variables for drawing output int _maxTimeDiv; //Max number of divisions to display on Output-Panel int _maxVoltDiv; //time axis = 15 divisions //volt axis = 4 divisions (2 positive Divs) // (2 negative Divs) int _ptsPerDiv; //How many points are there in 1 division. //1 point = 0.1 milimeter //Default 100 points = 1 division is 1 cm wide // ** Base on: Display Resolution= 1024 x 768 int _maxDrawPtsX; // _maxTimeDiv*_ptsPerDiv, Max Drawing Point for // time int _maxDrawPtsY; // _maxTimeDiv*_ptsPerDiv, Max Drawing Point for volt //Default x=1500, y=400 Copyright 2005 by Saksit Siriprayoonsak

EMGC Implementation: Draw Grid for Graph Output (cont.) Copyright 2005 by Saksit Siriprayoonsak

EMGC Implementation: Drawing Graph Output The output can be drawn by using (x,y) coordinate to specify position to draw. Function CEMGCDlg::voltToDC() Function CEMGCDlg::voltToDC() Copyright 2005 by Saksit Siriprayoonsak

EMGC Implementation: Saving Data Buffer To File File Extension (‘.emg’) Header line contains Sampling rate (HZ) Record time period (sec) Data speparate by a ‘space’. Each record separated by a ‘carriage return’ (put in front). Copyright 2005 by Saksit Siriprayoonsak

EMGC Implementation: Read File To Data Buffer Read header file Sampling rate -> computes sampling period Record time period -> verifies the data file (completed or in completed) Store data in buffer (dumpDataArray) struct SOutputData { int output_ii; //Iteration start from 0 double time; //Time stamp in Second double volt1; //Voltage value for CH1, CH2, CH3, and CH4 double volt2; double volt1; }; CArray <SOutputData, SOutputData> dumpDataArray; Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak Results Our EMG Amplifier ME3000 Muscle Tester ME3000-Muscle Tester Manufactured by Maga Electronics Ltd. Displayed by using program VIEW version2. A comparison of cylindrical grasp recorded from our EMG amplifier and ME3000. Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak Results (cont.) Our EMG Amplifier ME3000 Muscle Tester ME3000-Muscle Tester Manufactured by Maga Electronics Ltd. Displayed by using program VIEW version2. A comparison of preshaping of cylindrical grasp recorded from our EMG amplifier and ME3000. Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak Conclusion This thesis presents an implementation of EMG amplifier device and EMG Capture program. Major problems were: To reduce noise, moving artifacts, system grounding and DC bias. Problems solved through: Proper choice of discrete components (resistors, capacitors, and ICs) Proper design of circuitry Final implementation of the device using PCB technology Systematic experimentation with the prototype (implemented on a breadboard) Extensive testing of the device after implementation and executing final corrections. Copyright 2005 by Saksit Siriprayoonsak

Copyright 2005 by Saksit Siriprayoonsak Future Work EMG amplifier Smaller size of the housing unit. Eliminate electrode extensions EMG Capture program Add print feature Add properties feature for changing system parameters Improve drawing ability Copyright 2005 by Saksit Siriprayoonsak