| Currently,the number of patients with hemiplegia caused by stroke and spinal injury is increasing,and they need to be treated by external rehabilitation electrical stimulation systems.However,most of the commercially available electrical stimulation systems only produce a single waveform of electrical stimulation pulses,which cannot achieve the best therapeutic effect.Foreign devices are versatile but expensive.Therefore,it is necessary to design a more functional,simple and economical electrical stimulation system for hemiplegic patients.To solve these problems,this thesis designs a functional electrical stimulation system that uses surface electromyography(sEMG)as the driver.The designed electrical stimulation system consists of a sEMG acquisition module,a microprocessor control module,an electrical stimulation module and a power supply module.sEMG acquisition module uses a series of low-cost operational amplifiers instead of foreign integrated chips to amplify and filter the collected sEMG.In order to solve the problem of high sEMG noise level caused by multi-channel acquisition and the use of low-cost op-amps,in the thesis an ensemble empirical mode decomposition(EEMD)method based on normalized index optimization(NIO)has also been designed to further reduce the noise of the original sEMG obtained from the acquisition module.The microprocessor control module uses the STM32F103 microcontroller to perform A/D conversion of the original sEMG and carries out on-chip noise reduction.Then the denoised sEMG is used as the driving signal for the electrical stimulation module,the reference voltage of the corresponding amplitude is output from the DAC port of the microcontroller according to its magnitude,and the pulse width modulation(PWM)signal is used to determine the frequency and pulse width of the stimulation pulse.The circuits of electrical stimulation module are designed to switch between the optocoupler and constant current source circuits under PWM control to output electrical stimulation pulses of suitable and variable amplitude,which are applied to the patient’s limb with the stimulation electrodes.In order to verify the practicality and reliability of the designed functional electrical stimulation system,a series of performance test experiments have been conducted.Firstly,the bandwidth of the band-pass filter circuit in the sEMG acquisition module has been verified to be 16 Hz～482 Hz.After that,sEMG of the small arm on a healthy limb has been acquired by flipping the wrist and making a fist with the acquisition module,and the experimental results showed that the sEMG acquisition circuit built with low-cost op-amps can obtain more accurate and useful EMG signals.Then,the noise reduction method has been studied on the PC host computer for the acquired original sEMG,and the normalized noise reduction seeking index r has been designed.Then the experimental noise reduction processing of sEMG using the EEMD method has been conducted.The performance of the designed algorithm is compared with several traditional noise reduction methods,and the index r=0.71 of the designed algorithm is better than all other methods.Finally,the performance of the electrical stimulation module has been tested.When the analog voltage of DAC input is varied from 0 to 3.3V,the module can generate biphasic stimulation pulses of about 0～165m A,the amplitude of which is determined by the size of sEMG after noise reduction,and the frequency and pulse width is determined by setting the PWM parameters of the microcontroller.The functional electrical stimulation system designed in this thesis is low cost,good performance,simple and practical.The functional electrical stimulation system designed in this thesis is low cost,good performance,simple and practical.It achieves the expected design index and has great market value. |
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