Electronic Muscle Stimulator

Abstract

An electric circuit arrangement for an electric muscle stimulator comprising a surging waveform generator, a pulse generator of higher frequency than the surging waveform generator, and a gating circuit connected to the surging waveform generator and the pulse generator and from which bursts of unidirectional pulses are obtained, the repetition frequency of the bursts being that of the surging waveform generator. A transformer has at least one primary winding and at least one secondary winding, the latter being connected to an electric muscle stimulator, and each burst of pulses is applied to the primary winding so that each successive pulse in each burst is an antiphase to its immediately preceding pulse thereby producing bursts of bidirectional pulses in the secondary winding.

Description

This invention relates to electric circuit arrangements for developing signals which may be used in an apparatus for stimulating muscles. These signals may be used therapeutically to stimulate muscles causing them to contract, as in normal exercise, and hence eventually to improve their "tone" or condition.

The degree of contraction of muscles thus stimulated depends to some extent upon the polarity of the signals applied to them and it is possible for a condition to arise when the stimulating signal is applied symmetrically from a pair of electrodes in which the contractions which are produced are not symmetrical, due it is believed, to a kind of polarizing effect.

The present invention is concerned with the provision of circuit arrangements, the use of which makes the occurrence of this condition less likely.

According to the present invention there is provided a circuit arrangement for an electric muscle stimulator including a surging waveform generator, a pulse generator, a gating circuit, a connection between the output from each of the two generators to the gating circuit, an output transformer, and a connection to the input of the transformer from the output from the gating circuit, the gating circuit being controlled by the surging waveform generator in such a way that the output from the gating circuit includes signals at the pulse generator frequency in bursts which are controlled in accordance with the output of the surging waveform generator, and the transformer being so arranged and connected that the output from the transformer includes alternate pulses of opposite polarity at the pulse generator frequency.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 shows a block schematic diagram of one circuit arrangement;

FIG. 2 shows the waveforms of signals occurring at various points in the arrangement of FIG. 1;

FIG, 3 shows the detailed circuit of a part of the arrangement shown in FIG. 1;

FIG. 4 shows the waveforms of signals occurring at various points in the circuit of FIG. 3;

FIG. 5 shows a block schematic diagram of another circuit arrangement;

FIG. 6 shows a detailed circuit of the arrangement illustrated in FIG. 5;

FIG. 7 shows the waveform of signals occurring at various points in the circuit of FIG. 6; and

FIG. 8 shows a block schematic diagram of a further circuit arrangement.

Referring to FIG. 1 there is shown a surging waveform generator 1 the output of which is applied to a mixer stage 2 via a lead 3. An output from a square wave generator 4 is also applied to the mixer stage 2 via a lead 5. The output from the mixer stage is applied via a lead 6 to an output stage 7. Referring to FIG. 2 there is shown at (a) the output from the surging waveform generator 1 and at (b), to a much larger scale, the output from the square wave generator 4. The output from the output stage 7, which is shown at (c) in FIG. 2, is unidirectional and when applied to muscles in this form it can result in the production of contractions which are not symmetrical.

In the arrangement shown in FIG. 1 however, the output from the stage 7 is connected via a lead 8 to a switch 9 controlled by a signal from the square wave generator 4 applied via a lead 10, a delay circuit 11 and a lead 12. The output from the switch 9 is then applied via a lead 14 to an output transformer 15 whose output is connected to electrodes 16.

Referring to FIG. 3 there is shown a detailed circuit including the delay circuit 11, switch 9 indicated by the dotted lines, and output transformer 15. Considering the circuit of FIG. 3 in conjunction with the voltage waveforms shown in FIG. 4, which waveforms are drawn against an exaggerated time scale in order that their relationship may be more clearly seen, waveform (a) represents the square wave signal which is received on lead 10 at the input to the delay circuit 11 from the generator 4. This signal is applied to a differentiating network formed by a capacitor 18 and a resistor 19 and the negative trailing edge of the differentiated signal is passed by a diode 20 to a monostable multivibrator including a transistor 21 and a transistor 22. The output from the collector of the transistor 22 and thus from the delay circuit is indicated at (b) in FIG. 4 and it can be seen that the signal has been delayed with respect to that which was received by the delay circuit on lead 10 and is indicated at (a).

The output from the delay circuit is applied over the lead 12 to the switch 9 having a bistable multivibrator circuit which includes transistors 23 and 24. This bistable circuit is switched by the trailing edges of the pulses from the monostable multivibrator in the delay circuit 11 and consequently the transistors conduct alternately for periods of time which are equal and comparatively long with respect to the periods of conduction of the transistors in the monostable multivibrator in the delay circuit 11. The switch further includes a transistor 26, a diode 27 and a transistor 28 connected to the output of the transistor 23, and a transistor 30, and a diode 31 and a transistor 32 connected to the output of the transistor 24. At (c) in FIG. 4 there is shown the voltage waveform of the signal appearing at the collector of the transistor 24 and from this it can be seen that there is a voltage rise when the transistor is switched off at the end of the output pulse from the delay circuit and a voltage fall when the transistor is switched on at the end of the next pulse received from the delay circuit. During the period when the transistor 24 is switched on the transistor 23 is nonconducting and vice versa. The transistor 28 is switched on while the transistor 23 is nonconducting and the transistor 32 is switched on while the transistor 24 is nonconducting. The emitters of the transistors 28 and 32 are connected to the output signal, illustrated at (c) in FIG. 2, obtained from the stage 7 via the lead 8. This signal on the lead 8 includes pulses, within the envelope defined by the output from the surging waveform generator, which are in phase with the output from the square wave generator. The transistor 28 is connected in series with one primary winding 33 of the output transformer 15, and the transistor 32 is connected in series with another primary winding 34 of the output transformer 15.

At (d) in FIG. 4 there are shown the voltage pulses appearing at the collector of the transistor 32 and at (e) in the same FIG. there are shown the voltage pulses appearing at the collector of the transistor 28 both of which result from the switching of the transistors 28 and 32 by the signals applied from the bistable multivibrator to their respective bases and the voltage pulses applied via the lead 8 to their emitters. The two primary windings 33 and 34 are wound in antiphase and the switching signals applied to the bases are delayed with respect to the signals on the emitters so that switching does not take place during the appearance of a voltage pulse on the lead 8. There are thus produced at the outputs of the secondary windings of the transformer 15 alternate pulses of opposite polarity as shown at (f) in FIG. 4. These pulses appear within the shape of the envelope of the output from the surging waveform generator as shown at (c) but both above and below the zero line. Signals applied to muscles via a pair of electrodes connected to any one of the secondary windings may thus be used to produce symmetrical contractions of the muscles.

Referring to FIG. 5 there is shown a block schematic diagram of an arrangement which includes a surging waveform generator 36 having an output similar to that shown at (a) in FIG. 2 which is applied to a gate circuit 37 via a lead 40. The output from a square wave generator 38 is shown connected via a lead 41, a bistable multivibrator 39 and a lead 42 to the gate circuit 37 and the output from the square wave generator 38 is also shown connected directly to the gate circuit 37 via a lead 43. Outputs from the gate 37 are applied via an output stage 45 to an output transformer 46.

In FIG. 6 the main circuit features described with reference to FIG. 5 are indicated by similarly referenced dotted lines. Referring to FIGS. 6 and 7 the surging waveform generator 36 is free running and includes transistors 47 and 48. The on-off periods of the transistors are determined by the values of the capacitors 49 and 50 and their associated resistors. The output from this generator is applied via a transistor 52 to give current gain over lead 40 to the gate 37. The square wave generator, which includes transistors 53 and 54, is also free running and its output is applied via the lead 41 to trigger a bistable multivibrator which includes transistors 55 and 56. The output voltage of the square wave generator 38 on the lead 41 is shown at (a) in FIG. 7.

The output signal from the transistor 55, which is shown at (b) in FIG. 7, is applied to the base of a transistor 57, acting as a gate, together with the signal on the lead 41 obtained from the output of the square wave generator, and applied via the lead 43.

The output signal from the transistor 56, which is shown at (c) in FIG. 7, is applied to the base of a transistor 58, acting as a gate, together with the signal on the lead 41 obtained from the output of the square wave generator and applied via the lead 43.

The voltage applied to the collector electrodes of the transistors 57 and 58 is the surging waveform signal generated by the generator 36 and applied via the lead 40.

The output from the collector of the transistor 57 is shown at (d) in FIG. 7 and the output from the collector of the transistor 58 is shown at (e) in FIG. 7. From these outputs waveforms it can be seen that square wave pulses are produced alternately from these transistors, the amplitudes of the pulses being controlled by the amplitude of the output from the surging waveform generator at the time.

The output from the collector of the transistor 57 is applied via amplifying stages, including transistors 60 and 61, to one half 62 of the center-tapped primary winding of the output transformer 46; and the output from the collector of the transistor 58 is applied via amplifying stages, including transistors 63 and 64 to the other half 65 of the primary winding of the output transformer 46.

The resultant output from the secondary winding of the transformer 46 is thus a train of pulses of alternate polarity, as indicated at (f) in FIG. 7, whose amplitude is controlled by the instantaneous amplitude of the output from the surging waveform generator 36.

Referring to FIG. 8 there is shown schematically a further arrangement by means of which there is obtained an output containing alternate square wave pulses of opposite polarity, the amplitudes of which are controlled by the instantaneous amplitude of an output from a surging waveform generator. The output from a surging waveform generator 68 is applied via a lead 69 to a mixer stage 70 and an output from a square wave generator 71 is applied via a lead 72 to the mixer 70. A second output from the square wave generator 71 is applied via a lead 73 to a delay and switch control circuit 74. The output from the mixer 70 is applied via a lead 75 to an output stage 76 and the output from the stage 76 is applied to the primary winding 77 of an output transformer a double-pole double-throw switch 78. The contacts of the switch may be operated by an electrical relay controlled, as indicated by the dotted line 79, by the control circuit 74. The load 81 is connected to a high-voltage source and an output is obtained from the secondary winding 80.

In operation the circuit is similar to that described with reference to FIGS. 1, 2 and 3 the electrical switch arrangement being replaced by a mechanical switch and the double wound primary winding being replaced by a single primary winding. It would be within the scope of the present invention to replace the mechanical switch by an equivalent electronic switch.

It is not essential that the generators 4, 38 and 71 should produce square wave pulses. It is possible to employ pulses having waveforms of other shapes.

It may be noted that the circuit is such that either of the pulse generators may be free running, although it is not essential that the generators should be of this type. They could be of the controlled type that is caused to operate in accordance with one condition of a switch and to be inoperative when the switch is in another condition.

The output of the surging waveform generator is arranged to have a leading edge which increases gradually in the way shown at (a) in FIG. 2 in order to provide an acceptable output signal and this waveshape may be controlled in a well-known manner by means of a resistor and capacitor connected in the generator circuit.

In a preferred embodiment the pulse generator has an "onto-off" or "mark-to-space" ratio of less than 1.

As may be seen from FIG. 3 the output transformer normally has a plurality of secondary windings and the output from each of these windings may be connected to a pad of electrically conducting material which then applied to the body of a person conducts the output signals from the transformer to the body in order to stimulate particular muscles of the person.

Claims

I claim:

1. A circuit arrangement for an electric muscle stimulator including:

a. a surging waveform generator, an output to the surging waveform generator;

b. a pulse generator of higher repetition frequency than said surging waveform generator, and output to the pulse generator;

c. a bistable circuit connecting said pulse generator output, and first and second outputs to said bistable circuit;

d. means for producing burst of unidirectional pulse generator pulses, said means comprising first and second transistors; base and collector electrodes to each transistor, the base electrode of said first transistor connected to both said first bistable circuit output and said pulse generator output, the base electrode of said second transistor connected to both said second bistable circuit output and said pulse generator output, said surging waveform generator output connected to both said collector electrodes;

e. a pair of muscle-stimulating electrodes; and

f. a transformer having a primary winding in the form of first and second parts connected in antiphase and a secondary winding connected to said pair of electrodes, said first part connected to said collector electrode of said first transistor, said second part connected to said collector electrode of said second transistor, whereby the output across said secondary winding comprises a train of pulse generator pulses of alternate polarity whose amplitude is controlled by the instantaneous amplitude of the output of the surging waveform generator.

2. A circuit arrangement for an electric muscle stimulator, including:

a. a surging waveform generator;

b. an output to said surging waveform generator;

c. a pulse generator;

d. first and second outputs to said pulse generator;

e. means connected to said surging waveform generator output and to said first output for producing bursts of unidirectional pulse generator pulses, the repetition frequency of the bursts being that of the waveform generator;

f. a pair of muscle-stimulating electrodes;

g. an output transformer;

h. a primary winding and a secondary winding to the transformer, said secondary winding being connected to said muscle-stimulating electrodes; and

i. means for applying the pulses of each burst in antiphase to each other to said primary winding comprising a double-pole, double-throw switch, moving contacts of said switch connected to said primary winding, fixed contacts of said switch connected to said means for producing bursts of unidirectional pulses; and a delay and switch control circuit connected to said second output of the pulse generator, said delay and switch control circuit controlling the actuation of said moving contacts in accordance with the pulse generator output; whereby the output across said secondary winding comprises a train of pulse generator pulses of alternate polarity whose amplitude is controlled by the instantaneous amplitude of the output of the surging waveform generator.

3. A circuit arrangement for an electric muscle stimulator, including:

a. a surging waveform generator;

b. an output to said surging waveform generator;

c. a pulse generator;

d. first and second outputs to pulse generator;

e. means connected to said surging waveform generator output and to said first output for producing bursts of unidirectional pulse generator pulses, the repetition frequency of the bursts being that of the waveform generator;

f. a pair of muscle-stimulating electrodes;

g. an output of transformer;

h. a primary winding comprising two parts connected in antiphase and a secondary winding to the transformer; said secondary winding connected to said muscle-stimulating electrodes;

i. means for applying the pulses on each burst in antiphase to each other and to said primary winding comprising a delay circuit connected to said second output of the pulse generator, a switch connected to said means for producing said bursts of unidirectional pulses and to said delay circuit, and first and second outputs of said switch connected to respective parts of said primary winding; whereby the output across said secondary winding comprises a train of pulse generator pulses of alternate polarity whose amplitude is controlled by the instantaneous amplitude of the output of the surging waveform generator.

4. An electric circuit arrangement for developing signals for use with an electric muscle stimulator, comprising, in combination:

a. a surging waveform generator;

b. an output to said surging waveform generator;

c. a pulse generator for producing unidirectional pulses;

d. a first output to said pulse generator;

e. means connected to said surging waveform generator output and to said first output for producing bursts of unidirectional pulse generator pulses, the repetition frequency of the bursts being that of the surging waveform generator;

f. a pair of muscle-stimulating electrodes;

g. an output transformer;

h. at least one primary winding and at least one secondary winding to the transformer, said secondary winding connected to said muscle-stimulating electrodes; and

i. means for applying each burst of pulses to said primary winding so that each successive pulse in each burst is in antiphase to its immediately preceding pulse thereby producing burst of bidirectional pulses in said secondary winding.

5. A circuit arrangement as claimed in claim 4, further comprising a second output to said pulse generator, and a bistable circuit connected to said second output of the pulse generator and to said means for producing bursts of unidirectional pulses.

6. A circuit arrangement as claimed in claim 5, in which said means for producing bursts of unidirectional pulses comprises a gating circuit having two outputs, and in which the primary winding comprises two parts connected in antiphase to the outputs of the gating circuit.