Electromyographic repetitive strain injury monitor
First Claim
1. An EMG monitoring device comprising:
- signal conditioning means, including rectifier and low pass filter means to produce a signal which is the envelope of an EMG signal being monitored, said filter means having a time constant on the order of 0.1 seconds,minimum signal detection means to produce a minimum level signal which tracks the minimum peaks of said envelope signal,minimum signal detection means including a low pass filter with a first time constant in the range of 1-2 seconds and rate limiting circuit means to limit the rate of change of the output of the minimum signal detection means in response to an increasing EMG envelope signal, the rate limiting circuit means having a time constant in the range of 5 seconds to 10 minutes such that the minimum level signal produced by said minimum signal detection means has a fast attack to the minimum value of the EMG envelope signal and a slow decay to the maximum value of the EMG envelope signal, andindicating means to indicate the difference between the minimum level signal and a predetermined threshold value.
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Abstract
A monitoring device for detecting muscle strain, which might lead to repetitive strain injury includes EMG sensors which generate an EMG signal, signal processing circuitry to derive a signal or signals representative of undesirable strain conditions and an acoustic signal generator which produces a signal to indicate when undesirable strain conditions exist. The signal processor includes a band pass filter to band limit the EMG signal, a rectifier and low pass filter to produce an envelope signal and a minimum signal level tracking circuit comprising amplifiers, capacitor, diodes and resistors. The minimum signal level tracking circuit produces a minimum level signal which tracks the envelope signal, with a short time constant while the minimum level signal is greater than the envelope signal, and with a long time constant when the minimum level signal is less than the envelope signal. The acoustic signal generator produces an acoustic alarm signal when the minimum level signal exceeds a preset threshold level.
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Citations
11 Claims
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1. An EMG monitoring device comprising:
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signal conditioning means, including rectifier and low pass filter means to produce a signal which is the envelope of an EMG signal being monitored, said filter means having a time constant on the order of 0.1 seconds, minimum signal detection means to produce a minimum level signal which tracks the minimum peaks of said envelope signal, minimum signal detection means including a low pass filter with a first time constant in the range of 1-2 seconds and rate limiting circuit means to limit the rate of change of the output of the minimum signal detection means in response to an increasing EMG envelope signal, the rate limiting circuit means having a time constant in the range of 5 seconds to 10 minutes such that the minimum level signal produced by said minimum signal detection means has a fast attack to the minimum value of the EMG envelope signal and a slow decay to the maximum value of the EMG envelope signal, and indicating means to indicate the difference between the minimum level signal and a predetermined threshold value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An EMG monitoring device comprising:
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first signal processing means for accepting an input EMG signal and for producing an EMG envelope signal representing the envelope of a filtered version of the input EMG signal; second signal processing means for accepting said envelope signal and for producing an output signal which (a) increases toward an upper limit with a first time lag and (b) decreases with a second time lag to closely follow said envelope signal when it is less than said output signal, said second time lag being substantially less than said first time lag; and indicator means for producing a humanly sensible stimulus in response to excessive excursions of said output signal.
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Specification