US2609499A - Muscle stimulator - Google Patents

Description

Sept- 2, 1952 w. E. GlLsoN Y 2,609,499

MUSCLE STIMULATOR Filed Sept. 27, 1950 OUTPUT Q. /o 93 JZ@ 'T' /zo 9066 /w /ZZ da@ v B+ B+ e, B+

544 B-Ol 1: v (Mr: (536 .#26150 .J we/,JMJ y wie yiwu/ Patented Sept. 2, 1952 r MUSCLE STIMULATOR Warren E. Gilson, Madison, Wis., assignor to `The Burdick Corporation, Milton, Wis., a corporation of Delaware Application September 27, 1950, Serial No. 186,997

This invention relates to apparatus for provide ing electrical impulses Vfor nerve and muscle stimulation. I 1 -v An object of the invention is to provide an apparatus for supplying muscle stimulating Yimpulses which are substantially faradic and which have extremely brief, high amplitude peaks of one polarity. l v

Afurther object of the invention is to provide an. apparatus for supplying repetitive muscle stimulating pulses of controllable amplitude.

A further object is to provide an apparatus supplying repetitive muscle -stimulating pulses having a cyclically rising and falling amplitude envelope.

A further object is to provide such an apparatus in which the amplitude envelope is generally sawftoothed.

A further object is to provide an apparatus for supplying muscle stimulating pulses having cyclically varying amplitude, the apparatus including means accurately and dependably to limit the maximum amplitude of the pulses.

'A still'further object is to provide an apparatus selectively operable to supply `relatively high frequency pulses of controllable amplitude, relatively high frequency pulses of cyclically varying amplitude, or relatively low frequency, constant amplitude pulses. Y

A stillY further object vis to provide muscle stimulating apparatus selectively capable of supplying muscle stimulating impulses'for either therapeutic or diagnostic purposes.

LPirther objects, advantages and principles of the invention will appear from the following description of an illustrative embodiment taken together with the drawing, which isa schematic wiring diagram of the embodiment.

' The illustrated embodiment of the muscle stimulator'inost conveniently receives its operating power from a 117 volt alternating current electric power line. 'In some cases the muscle stimulating pulses produced by the apparatus have the same periodicity as the alternating current voltage from the power line.

For this reason the muscle stimulator includes a peaking transformer iii] having its primary winding l2 connected with the 117 volt alternating current supply as indicated in the drawing. n I L `vThe transformer l is constructed in a'known manner to distort the essentially sinusoidal input wave form and produce a sharply peaked alternating current output-Wave form across these@-` ondary Winding i4 ofthe'ftransformer'. This'dis'- tortion is usually accomplished by designingth'e transformer so that partial saturation ofVr the magnetic core takes place on thepealrsA ofithe inputvoltage. Y L .f A One output conductor'ofrthe transformer sec,-

a third contact point |60.

e oiaims.; (c1. 25o- 27) ondary It is grounded and the other is connected with two contacts Ilia and 1Gb ofa single pole three-position switch It. The switch |16 has an arm I3 which is movable to make contact with eith'erof the contact points 56a or I 6b or with The movable arm I8 of the switch I6'i`sconnected with the grids of two arc discharge tubes or thyratrons 2t and 22 which are connected for parallel operation. The shield grids of the thyratrons 2e and 22 are connected to the cathodes, and the cathodes are connected in parallel.y A resistor 2e connecting the cathodes to ground provides cathode biasing voltage, and a second resistor 25 connecting the grids of the thyratrons to ground provides a grid return path.'

A resistor 28 connecting the cathodes with a suitable positive anode supply voltage terminal AB-lprovides a minimum cathode bias voltage 'suiiicient to prevent initiation of arc discharges in the thyratrons 2B and 22 in the absence of grid-cathode signals. A current flows from Blito ground through the resistors 28 andy 24 `and produces avcathode biasing voltage drop across the resistor v24..

The anodes of the thyratrons 20 and 22- are connected by low valuel current equalizing resistors 3G and 32 to one side of a primary wind'- 'ing 3A of a stepfup pulse output transformer 3E. The other `side of the primary 34` is connected with the cathodes of the thyratrons by a pulse forming capacitor 38. The same yside of the primary is also connected with a :positively charged conductor 46 by means of av charging resistor 42. The positive voltage appearing'upon the conductor it may vary, as will presently'be explained. e y,f

A high voltage secondary winding 44 of the .transformer 36 is shunted by a potentiometerd', .One side of the secondary M is grounded and is thereby connected with a grounded output ter',- minalli. A second output terminal 50 is conf nected by a current'measuring meter 52'with'the movable arm 54 of the potentiometer. Thepo'- tentiometer provides means to adjust the magnitude of the muscle stimulating impulses'suppllied to the output terminals 4S' and 5B by:y theap'- paratus.

-Whenthe movable arm i8 o-f the switchrll is brought into contact with either of the Contact points l 6a or 1Gb, the apparatus producesmuscle stimulating pulses at the Vfrequency of the 1147 -volt alternating current power-line. Of course .this frequency is usually cyclesper'second. During the negative half vcycle of thev sharply peaked alternating' current voltage produced'by the transformer'secondary It, the thyratronsI 20 vaudaz are nonconducting. The'capacitordijs vcharged through the resistor ft2 substantiallyato 40, and the voltage appearing across the capacitor 38 is applied to the anodes of the thyratrons by the transformerprimary 3'4 andthe current equalizingA resistors 30 and 32. The voltage drop across the cathode resistor 214 caused by the current flowing from the B+ terminal through the resistor 28 is sucient to prevent the voltage appearing at the anodes of the thyratrons from initiating arc discharges in the tubes.

The positive peaks of the alternating Ycurr-ent signal from the transformer secondary I4 raise the voltage between the gridsaand the cathodes of the thyratrons to such an extent that arc discharges are initiated in the tubes. When the discharges are started, v.the capacitor 38 discharges '.veryzrapidly '.through the 'circuit includingathezthyratrons;thefequalizing .resistors 30;and

SL-andztheitransformer primary :3 4.. 'Thetransformer primary .-34 and the-resistors 30 `and 32 have such' lowiimpedances thatathe dischargeof the condenser is not substantially impeded .or retarded.

diftertheadischarge-fof 'thercapacitor 38 thearc dschargesmi .the .thyratrons vfell and '22 are extinguishe'dlbecause the anode-cathode thyratron uoltagmdrops -toa -value insufficient to maintain vvthedischarges inftheatubes. :This occurs=at least partlybecause the-inductive transformer primary 34,;inrconjunction-with the-capacitor 38,-,tends to produce an oscillatory discharge current, Vand consequently tends Vto swing the anode -voltage of fthe .thyratrons -to aenegative value kmomentarily.

..iI-fheivalues ofthe-.input voltage tromthe transormcrfsecondary -l.-4, the cathode biasing voltageendthecapacitance ofthe capacitor 3.8V are selected 'so .that the grid-cathode .voltage .of ,the .thyratrons-has droppedsufciently to cut oithe `.thi/patrons:by-the time the condenser .38 hasidischarged through the thyratrons. Consequently, l:aisirlgle briefzcurrent. impulse .is produced through the primary3 o-tthe outputtransformer in synchronism .with each-.ofthepositive peaks .of the .input-voltage romthe transformer 14. IThe current-...impulses in 4the primary .34 .produce brief highvoltage .impulses k,across the .secondary 44 ofthe output y'transformer 36, and the voltage pulses, are ytransmitted to the output terminals thelpotentiometer .46.and thev meter 52. .Ater-the-.thyratrons. 28 aIidZZare-extinguished, .the--capacitor is. chargedrapidly through the resistor 42 to the positive voltage appearing on .the conductorll. The capacitorBB and the `resistor-'AZ- have small values, such. asf0.5 microfarad fand'finu: ohms, respectivelmso thatthe charging l ,time-'constant ,of .the capacitor and the resistor issmall with-respect to. the half period of the .input1.voltage.from the transformer Ill. In vthe above,` examplethei time constant. of the capacitor .and-.the resistor lis.2.0 `.milliseconds as compared withpproximately .8 milliseconds for ithe half period-.of the usual 60 cycle power line voltage. "The amplitude of the output voltageimpulses .is a function of the quantity of electrical charge storediinthecapacitor 38; whic-hin turnisa func- ,tion of .the .voltage appearingupon the-conductor 4.11. Ihevoltage on the conductor dil is controlled hy.rneans of apair of vacuum discharge-coupling tuiles.' 60 and'ii2` having their cathodes connected ltothe conductor 140. The tubes Eiland 62 preferably are pentodes of thetype commonly used in the ,power output stages of radio receivers.

However, the tubes Yare operated as triodes by connecting theirl screen grids to their anodes. 'lhejanodes 'are Aconnected directly to a Asuitable 'anode voltage supply terminal "B 4 The grids of the tubes 60 and 62 are connected with a movable arm 68 of a three-position switch .65 having three .contact points 66a, i611 :and 66a. 'Asindicated onthe drawing, the switch 6B may be ganged with the switch I6.

'The first contact point 66a is connected with a potentiometer 10 through a current limiting resistorTZ. 'The potentiometer T0 comprises a Plu- :rality- :of resistance elements 14, illustrated as yeight 1in number, .connected in series between a suitable positive anode voltage supply terminal is adjustable by means of a multi-position switch havingan arm 'I8 movable into contacting engagement with any one-of a plurality of contact points 80 respectively connected with -the end pointsI ofthe resistors. 14. f

The conductor 16 is connected tota .slider 18.0 of --a .voltage `dividing vresistor d2 to impress .an adjustable .relatively low positive voltage upon the-conductor. .The voltage'dividing resistorZ isfgrounded .at .one-.end and .is connected t.with an anode voltage terminal B+ at the other .end by-.means of altering resistor 84. The voltage .ditiding resistor .82 .is ,bypassed by anltercapacitor 8.6. .As indicated,.the negative terminal.B- of v.the .anode voltage supply (not shown) iS grounded.

The iirst ,contact point aofthe switch 6.6 is connected through the resistor l2 with .the switch arm .18 .of .the .potentiometer T0 `and is bypassedtothe conductor i6-by a filter capacitoriBU.

When .the .switch .arm '.68 is .brought .into contacting engagement with the rst .contact VVpoint 66a, the `grids .of the coupling .tubes .6.0 4and .62 are ,connected with thepOtentiometer lil., Land the voltage. of .the grids caninev varied'between. the voltage of theanode. supply .terminalB-lrand the voltage appearing upon the conductor .16, vvwhich isdeterminedbythe adjustment .of the slider '.80 on .the voltage divider .82.

The voltageappearing .upon .the conductor 40 connected with the cathodes of the coupling-.tubes .Eiland 52 .tends to be-.approximately equal to the voltage Vimpressed .upon .the grids Vof, `the coupling tubes. .Any .rise .in .the cathode. voltage above the grid .voltage ,isinhibitedby .the .consequentrise. inthe cathode-grid .bi-as toward .the cut-01T value. Such a rise .in the cathode-grid voltage .is `eiective to .limit conduction. .by the coupling. tubes: 6 land 62.

On the other hand, .if .the vcathode 4vovltage Aoff thecoupling .tubes S0 and. .32 drops, .thecathodegrid voltage also .drops `and vtends to .increase .conduction inthe coupling tubes.

,Of .course the .capacitor ..38 is charged from the B-i-.terminal through the parallel coupling .tubes .6.0 and 62 .and the resistor 42. The extent to which the capacitor is charged. depends upon the .voltage applied tothe-grids of theI coupling tubes.

Consequently, Whenthe switch arms I8 .and .68 'are eset in. theirflrst positions .contacting .the switch f'poi-nts` Ha. and 66a, respectively, the muscle stimulator produces extremely brief imuscle stimulating pulses :at the frequency ofthe 1v1/7 volt tfic-C. power line. Thefiamplitude vof Ithe pulses dependsupon the voltage applied to the grids of the coupling tubes 6B and 62 by the'potentiometer lll. "Consequently, .the amplitude may bevari'edgmanually over a relatively wide range'.

'.When/thesswitch .arms I8 and 63 'are brought into contacting engagement with the .contact points; tlbzand:ibrrespectiyely; athirdithyratron 92 lisconnected into the circuit. "The thyratron92 provides'cyclical signals of generally Vsaw-toothed asta-46s@ wave form `forgvarying the amplitude envelope of the sharp impulses produced by the circuit compri-singv the thyratrons 29 and 22.

6311s :connected with the anode of the thyratron 92.` The anode of thethyratron 92 is connected with a suitable positive anode supply terminal B+ by'a relativelysmall value resistor 94, a'

conductor 95, and arelatively large value resistorp 'f The cathode of the thyratron'SZ is connected to ground bya resistor I and to an anode supply terminal B+ by a resistor |02. A current from the B+ terminal through the resistors |00 'and' |02 produces a voltage drop across the resistork which biases the cathode of the thyratron 92 withrespect to the grid.

The'cathode of the thyratron 92 is also connectedwith a movable'arm |08 of a switch |00 The vthyratron 92produces the sawt'oothed voltages by the alternate charging and discharging of the capacitor 0, when theswitch arm 5?v junction withrectier provide the B+ voltage.

The circuit including thefpentode |30 acts'tot limitthe maximum amplitude of the saw-toothed signal produced bythe thyratron 92A to the" apfproximate Value of the voltage appearing at the slider; |36 connected with the cathode o f the4 Ii'n'mediately after a 'discharge of thecapacitor, iiLthe grid of the pentodel30 isj pentode |30.

approximately atground potential because the grid isconnected bythe resistor |40 with theconductor 90. Consequently, the potential of the grid is approximately equal to the voltageacross' the capacitor ||0. At this time the voltage at the cathode of the pentode |30 is considerably greaterthan the Voltage at the grid, and the pentode |30 is thereby rendered non-conductive. 4v

IDB-,is moved finto contacting engagement with the contact 4point |0621'. The capacitor |0 is ch'arged'through the resistor 98 and is discharged through the resistor 94 and the thyratron 92. 'I'he resistance of the resistorl is much smaller than that of the resistor 98 so that the discharge off'the `capacitor is eiected in a brief interval,

compared with the time required for charging the capacitor.

The maximum amplitude vof the saw-toothedy voltage which appears at the anode of the thyratron 92, is closely regulated by arcircuit including a pentode of a type commonly employed ,for voltage amplification in radio receivers. vThe cathode Yof the pentode |30`is connected vwith the suppressor grid and is coupled with the con# trolgrid of Ythe thyratron 92 by a current limit--` ing capacitor |32. Thecathodeof the pentode |30 is connected bya relatively highv valuere# sister, y|341 with a second slider |30 contacting thevoltage dividing resistor 32. v

I'he screen grid of the pentode |30is connected to an anode supply terminal`B+ by a resistor 3 8. The control grid of the pentode' is conf` nected through a current Alimiting resistor |40 Withthe conductor 96 in the anode circuit of the thyratron 92."

The anode of the pentode |30 is connected to a terminal v|442 of an alternating current voltage supply atapproximatelyv 300 volts. The other terminal |44 of the alternatingv current supply is grounded. rThe alternating current supply may provide a voltage at the frequency of the electric power line, and the 300 volt potential may easily be obtainedcfrom a high voltage secondary winding of l a transformer (not shown) connected with the ordinary 117 volt'power line.

The transformer may also be employed in con' As the capacitor H0 charges through the resisv tor 93 the potential ofv the grid of the pentode rises, and when the difference in potential be'- tween the grid and thel cathode of the pentode' |30 becomes less than the cut-off bia'svalue, the

pentode begins to'conduct 'on the peaks of thej positive half cycles of the alternating current voltage applied to the anode of the pentode. 'The momentary conduction in the pentode on Vthe positive peaks of the alternating current anode Voltage provides positive voltage impulses at the cathode of the pentode 'because of voltage drop across the load resistor |34.' The positivejim` pulses are coupled tothe grid of the thyratron 32y by the capacitor |32.y The capacitor |32 in cooperation with the grid return resistor |22 producesapulse sharpening effect.

one of the mst few pulses impressed upon niej control grid of the thyratron 92 causesinitiationf offan arc discharge in the thyratronJThe capacitor I9 disclriarg-esvv rapidly and the `pote nt 'ia.` 1 rv o f l the grid of the'pentode drops so that thel pentode is again'rendered nonconductive. The thyratron is extinguished when the capacitor ||l discharges to such 'an extent that 4the voltage; across the capacitor is insufiicient' to maintain conduction in the thyratron'.

Thus,A when the switch 'arms I3, 'andwlL make .contact with thesecond contact points |61), 65h 'and |0619.' respectively, the apparatus produces la series of 'sharp high voltage impulses at the frequency of the ||'|V volt supply, and the amplitude of the successive pulses cyclically increasesr and decreases in 'accordance with tl'ief saw-toothed Waveform, produced bythe tliyff ratron' 92."The sav/toothed voltageffrom' thyratron is impressed'upon the gridsof, the,

coupling tubes 60 and 62fthrough the second` switch'contact 36h. As previously explained,` the voltage on 'theconductor 110 which connects th coupling tubes withr the thyratrons, 2D and'22f1 varies in accordance with lthe voltageimpressed onthe grids of the tubes. i i .f

The 'capacitor H0 and the resistor 98 haye relatively high values such as 3 microfaradsa'nd 1f megohm, respectively, so 'that the` thyratron .192: produces 'a saw-toothed signal having a relatively lon'gperiod, ofja few seconds, for example.

When the switchy arms I8, 68 and |08 V'are brought into contacting vengagement vwithithe; third contact points IEC, A66C' and |06@ respectively, the capacitor l2 is connected inthe anode circuit of the thyratrcn'SZ.v The capacitance:off` the capacitor I l2 may be somewhat smallerithan'v the capacitance ofthe capacitor ||0 so that the thyratron 92produces a higher frequency sawj toothed signal when the capacitor 2 is inthe circuit. For example, the capacitance of the and lterV components to e values may be varied over Wide limits, particularly if compensating changes are made'ln other values. Resistance values are given in ohms and capacitance values in microfarads.

Resistors: f 24 2,200 26 100,000 28 270,000 n3|) and `32j. 5 42 4,000 46 10,000 T2 Y 100,000 14 n 270,000 82 25,000 8l 500 v94 1,500 sa 1,000,000 |00 2,700y |02 100,000 |272 500,000 V|34 50,000 |33 500,000 |40 1,000,000

Capacitors Tubes:

20 and 22 2D21 k 00` and 62 '7C5 -92 21321 l |30 AU'Gy While I have shown and described a preferred embodiment of my invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles of the invention. I, there-v fore, desire, vby the following claims, to include within the scope of the invention all such variations and modications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means. f What I claim is:

l. A ,muscle stimulator, comprising an impulse generator havingl output conductors for supplying muscle stimulating impulses and having a terminal, the potential of which determines the magnitude of the impulses; a saw-toothed wave modulation generator coupled to the terminal cyclically to vary the magnitude of the impulses, the modulation generator including al gaseous discharge` device having an anode, cathode and control grid, a circuit including a capacitor connected between the anode and the cathode, a direct current potential source, and a circuit including charging impedance connecting the source with the capacitor; a discharge tube having an anode, cathode and control grid; a circuit connecting the latter anode with the latter cathode including a supply of; cyclically varying voltage andaloadimpedance coupled with the grid of thegaseous discharge device; a circuit connecting the grid of the tube with the anode of the gaseous discharge device; and a direct current potentialsouree biasing the cathode ofthe discharge tube to a predetermined positive voltage value with respect to the cathode of the gaseous discharge device, so that thedischarge tube transmits an impulse from thev supplyeof cyclically varying voltage to the grid of the gaseous discharge device to trigger 'the llatter when the anode voltage of the gaseous'device approaches the predeterminedvalue. l' .f

2. A muscle stimulator, comprising an'impulse generator having output conductors for supplying muscle stimulating impulses and having a terminal, the potential of which determines the magnitude of the impulses; a saw-toothed wave device having an anode, .cathode and .A control Y grid, a circuit including a capacitor connected between theA anode and the cathode, a'. direct current potential source, and aV circuit including a charging impedance connecting the source with the capacitor; a discharge tube having an anode, cathode and control grid; a circuit connecting the tube anode with Vthe tube cathode including a load impedance coupled with the grid of the discharge device; a direct current potential source connected with the discharge-tube'to provide a grid-cathode bias of a predetermined value substantially` greater than suicient to cut orf the tube; a circuit connecting the grid of the tube with the anode of the device to render the tube conductive when the device anode voltage approaches the predetermined value of the bias.-v ing source; and a supply of cyclically varying voltage coupled to the tube to produce -anV impulse across the load impedance to render the discharge device conductive when theV tube'becomes conductive, so that the maximum device anode voltage is regulated approximately to Vcorrespond wth the predetermined value of Ythe biasing source voltage.

3. An apparatus to operate from an.' alternating current 'power line for producing muscle stimulating electrical impulses, comprising -a gaseous discharge device having an anode,-av cathode and arcontrol grid; a step-up output transformer having a primary Winding and havl conductive for discharging the capacitor abrupt;

ly, the transformer including a primary for 'con` nection with the alternatingcurrent power and a secondary connected with the grid and the cathode of the discharge device to furnishv peaked alternating current signals' to the device.

4. An apparatus to operate from an alternatling current power vlineLr'or producing'l..mu`scle stimulating electrical impulses, comprising a gas'- eous discharge device v'havinganV anode, fa 'cathl ode, and a control grid; a step-up output transformer having a primary winding and havinga secondary winding for supplying theV muscle stimulating impulses; a capacitor; a-discharge tube having an anode, a cathode anda control' grid; a direct current potential source; a circuit connected across the capacitor for charging the capacitor to a variable extent to control the nieguitudemf the.; muscle; stimulatingaimpulses, the circuitincluding Y a,Y direct current potential sourceY andgthe anodevand the cathode oi the tuheljn series with a` charging impedance; a source of variable, voltage connected *with the grid of the discharge tube to control vthe charging, ofthe. capacitor through the ,tube` and the charging impedance; a discharge circuit including;theprimary ofthe output transformer connectingcthe capacitor with the anodegandp cathode..of the v gaseous discharge device; and an inputgpeakingtransformer cyclically to render theY gaseous device ,conductive yfor discharging ther capacitor, abruptly; the transfornlervy includf ing.- a,-primary for connection with the alternat-v ing.; current power, Y line; andaA secondary ccnnected .With-the grid andcathode of the gaseous deycectorfurnish peaked alternating current signals to the device, A

. .5.: An.` .apparatus to operate ,from an. alternatlng: current icou/ er line. forA producing muscle stimulating, electrical impulses comprisingy a gaseous .discharge device having, en anode, a cathode. and a c control grid; asten-cup, output transfernierhavins a primary Winding and havllagseQQIldary Winding for supplyingthe muscle stimulatingimpulses; acapactcr; a circuittccnv nectedacrcss. they capacitor for charging the capacitcrto `avariable 4extent cycli/cally t0 vary the; magnitude of themuscle stimulating im: pulses, the circuit` including. a4 sclnce.v of.l a crclcally, varying positive SignalA connected in series. with. a, charging,impedanceiy the frecuency-,cf-the sienalbeingmuch less thantne impulse frequency. a discharging circuit includinglthc primary Y of; thel output transformer connecting thefcapactor with the .anode andcathcde of the discharecqdevice: and en.. input peaking transformer cyclically to render thegdischalgedevice conductvefor discharging thecapacitor abruptlinthe transformer including a primary for ccnnect'cn with the. .alternating current power line end.a;-;seccndary connected with the. gridv and theocatlicdepof. thcdischarge device to furnish peaked-,4. alternating current signals. to, the. de: Vicec, Y Y 6cIrrenaimpulseprcducine.apparatus, asswtcothedwave generator including ai;gaseousdis-` charge. ,deyiceharing Y an anode, a cathode and centrclsrdi a. circuit including av capacitor. conn c tedbettveen theranode andtheccath/Qde; @directs currcnt. pctentalscurcc; a circuit including a; charging. o; impedance connecting. the. scurcewith thccepecitcr; Y a discharge tube having, anancdel a cathode and a, ,control grid;` a circuit connecting the tube anode Withthe tube cathode'including a load impedance coupled withlkthe grid of the gaseousY device; a direct current potential source connected with vthe discharge, tube to providea grid cathode bias of aV` predetermined value substantially greater than -f rsufficient to cut oir the tube; a'circuit connecting the grid of the tube with the anode of the gaseous device to lrender the tube conductive when the device anode voltage approaches the predetermined value of the biasing source; anda supply of'cyclically varying voltagecoupled to the tube to produce an impulse across the load impedance totrigger the gaseous devicewhen the tube becomesconductive, the cyclical period of the supply-'voltage being much less than the charging time constant of the capacitor'and the charging impedance, so that the maximum device anode voltage is Aregulated approximately to correspondwith thev predetermined,.V value, of? the biasing.:

source voltage.v

7. A muscle stimulator,A comprising; y discharge device having, an anode, acathodefand a control grid; aV step-up output transformer having a primary winding and having a secondary windingfor supplying the musclestimulating impulsesga capacitor; alcircuit-connected across the capacitor-for charging thecapacitor, including a direct current' potential source in series with a charging impedance; a d-ischarg ingY Ycircuit including'Y the V--transformerl primary connecting the capacitorA withY the anodeand cathode of the discharge device; a discharge tube having an anode, acathode and-Ya control grid; a direct current potential sourceconnected with the tube to provide agrid-cathode bias of a predetermined value substantiallyvgreater than suflicient to cut ofi-the tube; -a-second gaseous discharge device having an-anode, arcathode and a grid; a circuit connecting thetube-anode with the tube cathode including a loadimpedance coupled to the grid-of `the first and second gaseous devices; a second capacitor; a charging circuit connected across the second capacitor including; a direct current potential source and a second charging impedance in series, the time constant of the second capacitorand impedance being much greater than the time constant of the-.,rst capacitor andH impedance; a discharging circuit connecting the second capacitor with the second device anode and cathode; la circuit connecting the tube grid with the second device anode to render the tubeY conductive When the second device anode voltage approaches the bias value; and a supply of cyclically varying voltage coupled to the tube to-produce an impulse across the load impedance torenderthe first and second devices conductive momentarily whenY the tube becomes conductive, the cyclical supply voltage period being substantially .less `rthan the time* constant of the second capacitor andi-impedance.

8. A muscle stimulator for producing. either high frequency electrical impulses varying, cyclically in amplituderor low frequencyimpulsesj having; constanteamplitude comprising an im pulse generator for producing the muscle. stimulating impulses in responseto input signals. the generator having-an input, terminal for rc1. ceiving the input signals and a control terminal. the potential of which determinesithe amplitude of the impulses; a constant potential; supply an oscillator for producing relatively low frequency saw-toothed Waves; a sharpening circuit coupled to the oscillator for producing sharp impulses. in

synchronism with the saw-toothed Waves; a.

source of relatively high frequency signals;4 and a two-pole switch having a rst position for Vcorinecting thefinput terminal with thesource and for connecting the control terminal with the oscillator and having a second positionfor con.- necting the input terminal with the Asharpening circuit andrconnecting the control terminal with the supply.

WARREN E.v GLILS'OlSI;j'4

REFERIVINCESv CITED The following references are -of recordi in the le of this patent:

UNITED STATES PA'IEN'IS Number Name Date 2,496,543 Kanner Feb. 7,1950 2,511,595 Loughren Y YJuner13v, 1950,

a; gaseous

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