US3883900A - Bioelectrically controlled prosthetic member - Google Patents

Abstract

A prosthetic arm has an upper arm member having a stump receiving socket, a forearm member and an elbow unit secured to the upper arm member and pivotally connected to the forearm member. A drive, housed within the elbow unit, includes a reversible direct current permanent magnet torque motor and a transmission including a planetary gear reduction unit, a reverse locking clutch, and a plano-centric unit and the transmission is connected to the forearm member with its output shaft part of the pivotal connection therewith. The forearm member houses a battery pack and the circuitry by which the motor is operated in either direction in response to electromyographic signals that may be picked up from the biceps and triceps by electrodes when attached to the stump and processed to drive the motor in a direction and at a rate dependent on the dominant EMG signals. The locking clutch is operable to hold the arm flexed against a predetermined load and the elbow unit also houses a tachometer to provide a feedback to modify the power supplied to the motor to enhance the controlability of the amputee of flexing velocities.

Description

United States Patent J erard et al.

[ BIOELECTRICALLY CONTROLLED PROSTHETIC MEMBER Inventors: Robert B. Jerard, Brattleboro, Vt.;

Cord W. Ohlenbusch, Hopkinton, Mass Liberty Mutual Insurance Company, Boston, Mass.

Filed: Sept. 7, 1973 Appl. No.: 395,236

[73] Assignee:

US. Cl 3/l.1; 3/l2.3 Int. Cl A6lf l/06; A6lf l/OO Field of Search 3/1.1, 1212.3

References Cited UNITED STATES PATENTS 1/1971 Ohlenbusch et al. 3/1.!

Primary Examiner-Ronald L. Frinks [57] ABSTRACT A prosthetic arm has an upper arm member having a stump receiving socket, a forearm member and an elbow unit secured to the upper arm member and pivotally connected to the forearm member. A drive, housed within the elbow unit, includes a reversible direct current permanent magnet torque motor and a transmission including a planetary gear reduction unit, a reverse locking clutch, and a plano-centric unit and the transmission is connected to the forearm member with its output shaft part of the pivotal connection therewith. The forearm member houses a battery pack and the circuitry by which the motor is operated in ei' ther direction in response to electromyographic signals that may be picked up from the biceps and triceps by electrodes when attached to the stump and processed to drive the motor in a direction and at a rate dependent on the dominant EMG signals. The locking clutch is operable to hold the arm flexed against a predetermined load and the elbow unit also houses a tachometer to provide a feedback to modify the power supplied to the motor to enhance the controlability of the amputee of flexing velocities.

21 Claims, 14 Drawing Figures iZUENTEU N- SHEET10F 8 PMEMEDH 3.883.900

SHEET 2 OF 8 FIG. 4

1 BIOELECTRICALLY CONTROLLED PROSTHETIC MEMBER BACKGROUND OF THE INVENTION For several years, it has been apparent that bioelectric control of prostheses would be highly advantageous as such control could be similar to the control of the corresponding body section lost through amputation. The muscles of the stump produce electrical signals which can be sensed directly from the surface of the skin. Such signals are called electromyographic signals and are herein often referred to as EMG signals.

In U.S. Pat. No. 3,557,387 dated Jan. 26, 1971, a joint prosthesis is detailed in which such signals are effectively utilized to control the flexing of a forearm member with the advantage generally referred to above. The forearm member housed the motor, the transmission, an electromechanical brake, and the circuitry while the current demands were such that the power source had to be external due to its size and weight.

In general, prosthetic arms in which flexing is effected by EMG signals have had transmissions that were relatively heavy and bulky and additionally were not as smooth and quiet in operation as desired. Evaluations and suggestions by amputee users have pointed to a need for a decrease in weight and noise and a smaller, less cumbersome battery pack.

It should be here noted that proposals have been made to use plano-centric drives in prosthetic arms. See Livingston S.M., D. I. Crecraft, Design of an Artificial Elbow; an Electromechanical Solution, Control of Artificial Limbs, the Institution of Mechanical Engineers, London 1968.

While plane-centric drives offer advantages in size and strength, they have been excessively noisy at high speeds and run very roughly at low speeds.

THE PRESENT INVENTION The general objective of the invention is to provide a jointed prosthesis of appropriate weight and weight distribution with flexing responsive to EMG signals derived from the stump to which the prosthesis is attached and with the actuating mechanism, the circuitry, and the power source all contained within the prosthesis.

This general objective is attained by providing a prothesis with a joint unit housing a motor and transmission. The joint unit is secured to one member with the output shaft of the transmission connected to the other member in a manner such that said other member is flexed in a direction dependent on the direction in which the motor is operating with the transmission providing a substantial gear reduction between the motor and the driven shaft and including a reverse locking clutch to enable the prosthesis to be locked in a flexed Another objective of the invention is to provide a locking clutch that overcomes problems of previous brakes that may be summarized as over-riding load chatter, an objective attained by providing a clutch that becomes operative as a brake by the jamming of rollers as a consequence of a load but with instant locking prevented by including in the clutch frictionally engaged surfaces. The tachometer controlled velocity feedback is operative to place the motor in operation at a rate commensurate with that wanted by the ampu- Other objectives of the invention are to enable the amputee to have better control of flexing velocities and to enable starting friction to be readily overcome, both objectives attained by the use of a tachometer coupled to the motor and providing a velocity feedback effecting appropriate modification of the power input to the motor.

Another objective of the invention is to provide for further conservation of power by the use of limit switches arranged to prevent overtravel of the flexed member of the prosthesis in either direction and to permit the prosthesis to remain in its fully extended or its fully flexed position without the motor drawing battery current.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, a preferred embodiment of the invention is shown, and

FIG. 1 is a side view of a prosthetic arm in accordance therewith;

FIG. 2 is an exploded view of the elbow unit showing the components housed therein;

FIG. 3 is an exploded view of the transmission showing its components;

FIG. 4 is a section, on an increase in scale, taken lengthwise of the elbow unit along the axis of its connection with the forearm section;

FIG. 5 is a section taken approximately along the indicatedline 55 of FIG. 4 showing the planetary gear- FIG. 6 is a section taken approximately along the indicated line 6-6 of FIG. 4 showing the reverse locking clutch;

FIG. 7 is a section taken approximately along the indicated line 77 of FIG. 4;

FIG. 8 is a section taken approximately along the indicatedline 88 of FIG. 4;

FIG. 9 is a block diagram of the mechanical and electrical components;

FIG. 10 is a schematic view of the EMG amplifiers and the EMG signal processing;

FIG. 11 is a like view of the signal summer and the velocity feed back amplifier;

FIG. 12 is a like view of the pulse width modulator FIG. 13 is a schematic view of the battery filter; and

FIG. 14 is a like view of the power amplifier.

An artificial arm in accordance with the invention includes, see FIG. 1, a conventional upper arm section generally indicated at 15 with parts of its attaching harness indicated at 16 and 17. Thearm section 15 has anend plate 18 at its distal end.

A forearm section, generally indicated at 19, has ashell 20, shown only in phantom, enclosing a frame which consists ofsides 21 and 22 in support of aplate 23 for circuit boards indicated generally at 24 and 25 and afront end wall 26 to which aholder 27 is attached, theholder 27 providing support for a terminal device, such as theconventional hook 28. Theholder 27 is detachably attached to theend wall 26 and its length is determined by the forearm length appropriate for each amputee. At their other ends, thesides 21 and 22 have transverselyalignedholes 29 and 30, respectively, thehole 29 round and thehole 30 square. Adjacent said other ends, theframe sides 21 and 22 support aholder 31 of U-shaped cross section for the support of the battery pack 32'.

Thearm sections 15 and 19 are interconnected by a prosthetic elbow unit generally indicated at 33 in FIG. 1 and, as shown inFIGS. 2 and 4 it has a housing formed in two parts, thepart 34 and thepart 35 clamped together byscrews 36. A reversible direct current, permanent magnet torque motor, a tachometer,

generally indicated at 37 and 38 respectively, and a transmission later to be detailed are within the housing. Thehousing parts 34 and 35 havesurfaces 34A and 35A that are coplanar when the housing is assembled and seat against theupper arm plate 18 with thehousing surface 34A provided with a threadedstem 34B by which theelbow unit 33 is attached to theplate 18 of theupper arm section 15. Thehousing part 35 has an internal,annular recess 35B for an internally toothed rim gear orcircular spline 39 clamped between thehousing parts 34 and 35 and held against turning relative thereto as by thescrews 36.

Thedrive shaft 40 of the transmission is rotatable in the end wall of thehousing part 34 and has an outwardly disposedsquare hub 40A fitting thesquare hole 30 of theframe side 21 which is locked thereto by ascrew 41 and an interposedwasher 42. Thehousing part 35 has anchored therein an outwardly disposed axial, internally threadedinsert 43 extending through thehole 29 of theframe side 22 and locked thereto by ascrew 44. On both sides of theunit 33 there is astop 45 engageable by the proximate frame end to limit the extent to which theforearm section 19 can be flexed or straightened. In practice, the arc through which the forearm section may swing is 130.

Thedrive shaft 40 has a flange 40B at its inner end clamped to the end wall of thecasing 46 of themotor 37 and the interposed end wall of theflexible spline 47 byscrews 48. At its other end, thespline 47 has a series of lengthwise teeth or splines 49 meshing with the rim gear or fixedspline 39 in a manner subsequently detailed.

Within thecasing 46 is thestator 50, thebrush ring 51 and therotor 52 of themotor 37 with the ends of therotor shaft 53 supported by ball bearing units 54, one fixed in the end wall of themotor casing 46 and the other in itsend cap 55 which with an internallytoothed ring gear 56 and anouter clutch housing 57 are clamped to the open end of thecasing 46 byscrews 58.

The end of thedrive shaft 40 and the end wall of themotor casing 46 have sockets defining achamber 59 for thetachometer 38 whosecoupler 60 is entrant of abore 53A on the proximate end of themotor shaft 53 and establishes a rigid coupling therewith.

The planetary gear reduction unit or section of the transmission, see FIGS. 4 and 5, includes thering gear 56, aclutch housing 61 having a flange 61A clamped between thering gear 56 and the outerclutch housing 57. A rotatablecircular input plate 62 has a series ofgears 63 rotatably mounted thereon each in mesh with the drive gear 64 fixed on the end of thedrive shaft 53 of themotor 37 that extends through theend cap 55 and with the fixedring gear 56 so that theinput plate 62 rotates at a desirably reduced rate in either direction in which the motor is operated. In practice and by way of example, the ratio is 4.33:1. Theinput plate 62 has astub shaft 65 entrant of a socket in theshaft 66 of asquare output cam 67 which is a free fit within thehousing 61, theshaft 66 running inball bearing units 68 in the hub of theclutch housing 61.

Theinput plate 62 has two diametrically opposed pairs ofdrive portions 69 and 70, see FIG. 6, that are spaced apart with their outer surfaces arcuate and litting freely within thehousing 61 and their inner surfaces parallel to and receiving between them opposite sides of theoutput cam 67 and spaced relative thereto to provide a driving connection therewith. The arcuate extent of theportions 70 is greater than that of theportions 69 and aroller 71 is freely confined between thedrive portions 69 and 70 of each pair.

The transmission also includes a low ratio planocentric drive, see FIGS. 7 and 8, shown as a Harmonic Drive generally of the type disclosed in US. Pat. No. 2,906,143 and manufactured by USM Corp. of Boston, Mass. The drive has aflanged output hub 72 pinned to theshaft 66 and transversely slotted as at 73 to loosely receive the internally disposed, transversely alignedsplines 74 in the bore of acoupling 75 having aflange 76 and held in place by a retaining ring keeper 77 on the end of thehub 72. Thecoupling 75 has oppositely disposedexternal splines 78 each to fit the recess between the ends of circumferentially extendinginternal ribs 79 at one end of the wave generator plug 80 whose outer surface is elliptical as is apparent from FIG. 7. Aball bearing unit 81 has its races so made that the open end of theflexible spline 47 is thus made sufficiently elliptical to cause itssplines 48 to move into engagement with the internally toothed rim gear or circular fixedspline 39 in two opposed zones as is characteristic of such a drive, which in practice, provides a reduction in the order of 64:1.

With this transmission, when themotor 37 is operated to raise theforearm section 19, theinput cam portion 69 drives to theoutput cam 67 counterclockwise with therollers 71 held so that they cannot become jammed against thehousing 61. Similarly, when themotor 37 is reversed to lower theforearm section 19, theinput cam portion 70 drives theoutput cam 67 clockwise, after theinput cam portion 69 first dislodges therollers 71 if they have become jammed. If the arm is driving themotor 37 counterclockwise, theoutput cam 67 drives theinput cam portion 70 and therollers 71 cannot jam.

If, however, theforearm 19 is in a partly flexed position, whether or not in support of a load, theoutput cam 67 is biased in a clockwise direction thereby forcing therollers 71 to become jammed against thehousing 61. As stated earlier, thehousing flange 61 is clamped against thering gear 56 by the outerclutch housing 57 thereby to provide frictional resistance against the turning of thehousing 61 unless the load exceeds a predetermined value and should it move, thetachometer 38 senses such movement to bring themotor 37 back in service. i

'The main problem with reverse-locking clutches occurs with an over-riding load. For example, if the amputee wishes to lower a heavy load, two problems are present. The first of these is that when theinput cams 69 unjam therollers 71, theforearm section 19 instantly starts to take off" in the down direction with both the load and themotor 37 driving it. This effect is minimized by virtue of the fact the jamming angle is not less than l2.l4 nor more than 15.l4 which keeps the motor torque necessary to unjam therollers 71 to a minimum. Thetachometer 38 then provides the velocity feedback necessary to reduce the power to themotor 37 to prevent the take off.

The second problem results from the fact that theoutput cam 67, being unsupported and free to move in the-same direction as the input cams are travelling, now jams therollers 71 back against thehousing 61. Theinput cams 69 immediately unjam therollers 71 and the repeated jamming and unjamming results in a chatter effect as the amputee lowers the load. This effect is made minimal by the fact that the drive flange 61A is frictionally held by the pressure of the flange of theouter housing 57 as a disc brake, permitting a degree of slippage with chatter eliminated in the case of light to moderate loads and minimized in the case of heavy loads.

The overall functioning of the electronic circuitry is essentially the same as described in U.S. Pat. No. 3,557,387 but is quite different in order to achieve several additional desirable features. These features are lower power consumption, better common mode rejection, the incorporation of several deadbands whose use is subsequently described and better reliability. The overall functioning of this embodiment is described only generally in connection with, FIG. 9. The batteries of thepack 32 are of 6 volts and of the nickel cadmium type and provided with acolumbmeter 82 to allow the battery or batteries to be quickly recharged and the battery leads to thepower amplifier 83 are under the control of a manually operatedswitch 84. Normally closedlimit switches 85 and 86 are provided and these are positioned so that theswitch 85 is opened when the arm is fully raised or flexed and theswitch 86 is open when the arm is fully lowered or straightened.

In brief, in the case of the prosthetic arm herein described, the EMG signals are derived from the biceps and triceps by electrodes held in contact with the skin of the stump overlying those muscles. Such signals are alternating and relatively weak and must be rectified and suitably amplified. The circuit sections for thus processing EMG signals derived from the biceps and triceps are indicated at 87 and 88, respectively, see FIG. 10.

The electrical energy is applied to themotor 37 in pulses with their width determining the voltage signal to the motor. The polarity of the voltage input to themotor 37 and the width of the pulse is determined by EMG signals and the pulse amplitude is determined by thebattery 32.

The processed signals are combined in a summer, generally indicated at 89 and schematically detailed in FIG. 11 to provide a difference voltage orsignal representative of the strength difference between the processed input EMG signals. By way of example, the difference velocity is zero when the bicep and tricep signals are of equal magnitude. If the signal derived from the bicep is the larger, the prosthesis is flexed and if the tricep signals are the larger, a reverse or straightening movement results. Such combined signals are further processed by anamplifier 83, see FIG. 14, after modification by apulse width modulator 90, see FIG. 12.

Thetachometer 38 has its feedback connected to thesummer 89 to provide a signal proportional to the rate of movement, see FIG. 12. Reference'has already been made to the use of the velocity feedback to reduce the power to themotor 37 when a heavy load is being lowered. The velocity feedback from thetachometer 38 subtracts from the processed .EMG signals and acts to overcome the effect of the non-linearities in the friction of the mechanical drive system.

Below follows a detailed description of the electronic circuitry as shown in FIG. 10 through FIG. 14. Since the signal amplification and processing is the same for both the biceps and triceps, only the biceps channel is detailed but with the corresponding components of the triceps channel distinguished by the suffix addition vA to the appropriate reference numerals. The twobiceps electrodes 92 and 93 pick up the EMG signal from the biceps muscle surface from where it is conducted intoamplifiers 94 and 95. These amplifiers are unity gain followers and present a very high input impedance to the electrodes. The inputs of each of theamplifiers 94 and 95 are protected from excessive voltage surges by aresistor 96 in conjunction withdiodes 97 and 98 and said amplifier is stabilized against oscillation by acapacitor 99.

The output of each of theamplifiers 94 and95 feeds into anamplifier 100, the output of theamplifier 94 with a positive sign and the output of theamplifier 95 with a negative sign. Thus theamplifier 100 amplifies only the difference between these two signals and rejects any signal that is common to-both of them. The voltage gain ofamplifier 100 is 10 while the common mode rejection is 60 dB. The gain ofamplifier 100 is set byresistors 101, 102, 103, and 104. Means are provided to permit trimming of theresistors 101 or 102 to improve the common mode rejection beyond 60 dB.Capacitor 106 stabilizes theamplifier 100 whose output feeds through thecapacitor 107 and theresistor 108 and intoamplifier 109.

Theamplifier 109 serves several functions. It provides a high gain of up to 5,000 and filters out undesirable frequencies. Filtering networks are thecapacitors 107 and 110 and theresistors 108, 111, and 112 and thecapacitors 113, 114, and 115. Maximum gain of this amplifier stage is determined by theresistors 108, 116, 117, I18, and 111 and theresistor 118 is adjustable to permit some gain control. The output of theamplifier 109 is an AC signal proportional to the biceps EMG signal but amplified about 40,000 times. The same processing occurs in the triceps EMG amplifier and the amplified triceps EMG signal appears at the output ofamplifier 109A.

Rectification of these two signals is accomplished bydiodes 119, 120, 121, and 122 in conjunction with theamplifier 123. The bicep signal is full wave rectified with a positive sign and the triceps is full wave rectified with a negative sign. Since both rectified signals feed intoamplifier 123 its output produces the difference of these two signals. The output voltage is positive if the biceps EMG signal is stronger, the output is negative if the triceps EMG signal is stronger and the output is zero if both biceps and triceps signals have the same strength.Resistors 124 and 125, andcapacitors 126 and 127 set the gain ofamplifier 123 to 10 and provide filtering of any AC ripple remaining on the rectified signal. Thecapacitor 128 stabilizes theamplifier 123. Thediodes 119, 120, 121, and 122 also provide some incidental deadband effect due to the nonlinear characteristics of a semi-conductor diode. The deadband discriminates against 60 Hz interference signals because it is sensitive to the peak value of voltage. 6OHZ interference signals are essentially sinusoidal in shape while EMG signals contain many voltage spikes. Thus for the same voltage average of 60 Hz and EMG the EMG will have much higher voltage spikes the tips of which would pass through the deadband while the 60 Hz sinewave amplitude would not be high enough. This and other deadbands will be described later.

FIG. 11 shows the circuitry required for the nonlinear filter, the velocity amplifier, and the summary amplifier of thesummer 89.

The EMG signal contains a large amount of random amplitude variation even if the muscles producing the signals are under relatively constant tension. Since it is desirable to hold the elbow stationary for some tasks,

and fast amplitude variations improves the control of i the elbow appreciably. The filter uses the nonlinear V-I characteristics of di odes 129, 130, 131, and 132 in conjunction with acapacitor 133. Anamplifier 134 is used as a unity gain follower providing very small loading for the filter. The time constant of the filter is determined by the effective resistance of the diodes which in turn depend on the diode current. For sudden large input voltage changes the diode current is high and the resulting time constant will be small. For a small and slow input voltage variation, the time constant is large. Upper and lower limits on the time costant are provided by theresistances 134 and 135. The amplifier is stabilized by' acapacitor 137. A second deadband is produced by thediodes 138 and 139. a

The velocity signal amplifier 140 receives its input signal from the tachometer38. The amplifier l40has a gain of one-half which is set byresistors 141 and 142 and acapacitor 143 stabilizes the amplifier 140.

The summingamplifier 144 of thesummer 89 combines the processed EMG signal and the velocity signal in the proper proportion as determined by theresistors 145 and 146 and aresistor 147 sets the gain of the am plifier 144 and thecapacitor 148 stabilizes it.

Thepower amplifier 83 receives the signal from the summingamplifier 144 and drives thetorque motor 37 proportionately. To minimize power losses in thepower amplifier 90, it operates in a switching mode. Its outputs are voltage pulses of constant amplitude and repetition rate but varying in width according to the input signal. Theamplifier 83 can be separated into sections having functions: (1) the pulse width modulator 90A, see FIG. 12, (2) the polarity sensor, (3) the power switching amplifier, the circuitry shown in FIG. 14.

FIG. 12 shows the circuitry necessary to convert the output of the summingamplifier 144 of FIG. 11 into the pulse width modulated signal required to drive themotor 37. To simplify the switching amplifier and pulse width modulator design, the output from summingamplifier 144 is split into an unidirectional amplitude signal and a polarity signal. The amplitude is pulse width modulated, while thepolarity signal determines the direction of current through the motor. Both of these functions are accomplished with theamplifier 145. A-

unidirectional amplitude signal is obtained by rectifying the incoming signal from the summingamplifier 144 output. The rectification is obtained by thediode 146 and the use of the base-emitter diode of atransistor 147. These two diodes create a half wave rectified signal at the junction of thediode 146 and aresistor 148. Full wave rectification of the signal occurs at the junction of theresistors 149 and 150.Resistors 151 and 148 set the gain of amplifier and thecapacitor 152 stabilizesamplifier 145.

The polarity signal is generated bytransistor 147. When the base-emitter diode of thetransistor 147 conducts, i.e., when the input to theamplifier 145 is positive a current will flow in theresistor 153, turning on thetransistor 154 and causing signal P+ to go positive. At the same time signal P- will go towards ground. When'the input signal to theamplifier 145 is negative the current through the base-emitter diode of thetransistor 147 will go to zero and will cut off, letting point P- rise toward +5V and causing P+ to fall to ground potential. Aresistor 155 provides a path for the base leakage current of thetransistor 154 while theresistor 156 acts as the collector resistor.

Pulse width modulation is accomplished by theamplifier 157 which compares the rectified output of theamplifier 145 with a triangular wave generated by theamplifiers 158 and 159 When the triangular signal exceeds the rectified signal the output of theamplifier 157 will be negative. When the. rectified signal exceeds the triangular wave the output of theamplifier 157 .Will be positive. The output of theamplifier 157 will thus be a square wave of constant amplitude, with the same frequency as the triangular wave and a pulse width proportional to the amplitude of the rectified signal.

.The triangular signal is generated by theamplifier 158 which is an integrator and by theamplifier 159 which is a comparator, the former using aresistor 160 and acapacitor 161 to generate a ramp whose slope depends on the polarity of the current flowing through the resistor'160. When the voltage at the output .of thecomparator amplifier 159 is positive, current will flow into terminal No. -2 of theamplifier 157 and the ramp will have a negative slope. The output of theamplifier 157 is compared against a signal derived from the output of theamplifier 159 throughresistors 162, 163, and 164 anddiode 165. When the ramp signal falls below the reference voltage level established by theresistors 163 and 164 and thediode 165, thecomparator 159 will switch to a negative and cause a negative reference voltage level and also reverse the direction of the current in theresistor 160. The triangular signal excursion extends from0 volts to some positive level with its zero level determined by theresistors 163 and 164 and thediode 165. This switches the integrated signal from a negative to a positive slope with the output of theamplifier 158 rising. When the output of theamplifier 158 rising. When the output of theamplifier 158 overcomes the reference voltage the output of theamplifier 159 will switchpositive again and the cycle will repeat. Thus the output ofamplifier 15 becomes a triangular signal. Aresistor 166 provides a matching input impedance for the terminal No. 3 of theamplifier 159 while acapacitor 167 stabilizes the amplifier. Theresistor 163 establishes a negative bias for the reference voltage of theamplifier 159. This creates a deadband for the pulse width modulator.Resistors 168 and 169 adjust the amplituce of the triangular signal to its proper level.

In FIG. 13, a battery filter is shown havingresistors 170 and 171 andcapacitors 172 and 173 to filter the battery voltage to prevent noise from entering the operational amplifier circuits.

The switchingamplifier 83 shown in more detail in FIG. 14 must serve two functions. It must control the total power applied to themotor 37, i.e., the elbow torque and it must also control the polarity of this power, i.e., the direction of the torque. Power flowing into themotor 37 is controlled by four power transistors which operate in pairs. When thetransistors 174 and 175 are conducting themotor 37 will drive theelbow unit 33 in a flexing direction. When thetransistors 176 and 177 are turned on, themotor 37 will drive theunit 33 to extend or straighten theforearm 19. A flip-flop comprised oftransistors 175 and 178 decides which power transistor pair controls the motor power. Action of the flip-flop will be described later.

The amplitude of the motor current is controlled by the on-time of the power transistors which again is a function of the pulse width modulator signal derived from the output of theamplifier 157, see FIG. 12, and is applied through theresistor 180 to the base of thetransistor 181. When this signal is positive, the transistor will turn on pullingresistors 182 and 183 to ground. This will turn on thetransistor 184 or thetransistor 185 depending on the state of the flip-flop. Assume that thetransistor 184 turns on, the current will flow through theresistor 186 and thetransistor 187 will turn on to turn on thetransistor 187 directly and the transistor 174 through theresistor 188.Resistors 189, 190, 191, 192, 193, 194, and 195 are base leakage resistors.Resistors 186, 196, 197, and 188 limit the current flow.Diodes 198, 199, 200, and 201 are flyback diodes which provide for continuity of the current through the motor inductance during the switching interval thus protecting the power transistors from high voltage spikes.

The flip-flop, thetransistors 175 and 178, is clocked or toggled by the leading edge of the pulse width modulator signal and its direction of toggle is determined by the state of the polarity signals P+ and P. If P+ is positive and P- is at ground potential every clock pulse will turn offtransistor 175 which will turn on thetransistor 178. If this was the state of the flip-flop before the clock pulse arrived no action will take place. If thetransistor 17 was turned on and thetransistor 179 was turned off before the clock pulse arrived, the clock pulse will toggle the flip-flop into its new state. Reversal of the polarity signals will cause the opposite behavior.Resistors 202 and 203 provide base leakage paths.Resistors 204 and 205 are the collector resistors for thetransistors 175 and 178, respectively.Resistors 206 and 207 provide the cross-coupling between thetransistors 175 and 178. The gating and trigger circuits uitlizeresistors 208, 209,diodes 210, 211, 212, and 213, and

Necessary to the objective of providing a jointed prosthesis of appropriate weight and weight distribution is a reduction in the weight of the battery pack and the recognition of the concept that, rather than to try to duplicate the action of a natural arm, the effort should be made to give the amputee the greatest functional capability with the least inconvenience.

Battery size and weight are determined by work requirements, for example, the maximum weight that is to be lifted in a predetermined time. The use of a purely mechanical, reverse locking clutch instead of an electro-mechanical brake cut in half the quiescent drain of the system and in combination with the improved circuitry, reduced the final quiescent drain to eleven milliamperes from an original 180 milliamperes. As a consequence, the standby operating time increased from 6 to 45 hours despite a reduction in the weight of the battery source from 3 /2 pounds to about 8 ounces, the maximum lift at 12 inches to be 5 pounds, and the speed between full flexion and full extension (without load) to be 1.0 second.

Extraneous EMG signals are, however, produced unconsciously by the amputee and these can easily produce momentary current drains in excess of 350 milliamperes making it essential to introduce a deadband into the signal processing system. Without such a deadband, current is delivered to the motor as a result of such extraneous EMG signals although the motor does not run as the motor does not produce enough torque to overcome starting friction. The object of the deadband is to provide, in brief, that zero effort provides zero current to the motor.

While thediodes 119, 120, 121, and 122 of theamplifier 123 incidentally delete some of the extraneous EMG signals an additional deadband is necessary for the effective control of such extraneous EMG signals. An effective deadband is, accordingly, provided before thesummer 144 by theparallel diodes 138 and 139.

A problem requiring an additional or second deadband is that DC drift and noise create signals from the junction where EMG and velocity feedback signals are summed by theamplifier 144. This additional deadband is found in the pulse modulator stage. The triangular signal excursion in the generation of triangular waves extends from aboutO volts to some positive level and its lower point is determined by the combination of theresistors 163 and 164 and thediode 165. Theresistor 163 biases the zero point to a positive value to eliminate the lower 10 percent of the summing voltage thereby providing a deadband to prevent small variations that might occur about the zero level.

The assignment of proper values of the second deadband is difficult due to conflicting requirements within the feedback loop of the system. On the one hand, it is desirable to make the deadband as small as possible to minimize its effect on the control of the arm. At the same time, the maximum allowable plant gain is directly determined by the magnitude of the deadband with a larger gain value resulting in the system being stiff with respect to velocity which is desirable as it eliminates the effect of stick-friction in the mechanical drive system.

A large deadband is desirable for good servo system characteristics. The relationship between the deadband value and the controlability of the arm is more difficult and is best determined in relationship to the mechanical deadband created by thefriction in the system and if less than that, say by one-half, the amputee will feel it as a slight increase in the mechanical deadband without noticeable loss of control. In practice, each deadband is in the neighborhood of percent of the maximum signal levels.

It will thus be appreciated that prosthetic joints in accordance with the invention are well adapted to meet the varied requirements involved in providing maximum functional capability with the least inconvenience to the amputee.

We claim:

1. A prosthesis comprising a first member having a stump receiving socket and provided with a support at its distal end, a second member, a joint unit secured to the support of the first member, a pivotal connection between saidjoint unit and the second member relative to said first member, a drive including a direct current permanent magnet motor and a transmission housed within the unit with the output shaft of the transmission so connected tosaid second member that said second member is flexed relative to said first member in a direction dependent on the direction in which said motor is operating, said transmission including first and second reduction stages and a reverse locking clutch between said stages operable under the conditions that the second member is in support of a load and the motor is not operating to move the member to raise or lower the load and electric circuitry including said motor, a battery, electrodes attachable to the stump and operable to detect EMG signals from the stump muscles that were used to flex and straighten the amputees missing joint, and signal processing means operable to convert the detected signals into signals that operate the motor in the direction and rate that corresponds to the strength of the dominant EMG signals.

2. The prosthesis of claim 1 in which the first stage is a planetary gear reduction unit and the second stage is a plano-centric drive.

3. The prosthesis of claim 1 in which the transmission also includes a friction brake that may slip to provide a cushion and the engagement of the reverse locking clutch.

4. The prosthesis of claim 1 and a direct current permanent magnet tachometer coupled to the motor and operable to provide a signal proportional to the rate at which said second member moves relative to the first member, the signal processing means includes means to amplify and convert the signals indicative of flexing to one polarity and those indicative of straightening to the other polarity, a summer operable to combine said signals to provide a difference signal, the tachometer provides a feedback signal proportional to the rate of flexing velocity, means summing the feedback and the difference signals to decrease the power input when said rate is greater than that intended by the wearer of the prosthesis, and a pulse width modulation and motor driving amplifier in which battery circuit determines the amplitude of the pulses.

5. The prosthesis ofclaim 4 in which the reverse locking clutch includes a friction brake operable, when a load is being lowered to cushion by slipping the reengagement of the clutch as the motor and the load alternatively release and lock the clutch.

6. The prosthesis of claim 1 in which the circuitry includes deadband means operable to exclude substantially all extraneous signals that would, when zero movement of the second member was wanted, cause battery drain.

7. The prosthesis ofclaim 6 in which the value of the deadband means is less than the mechaical deadband created by friction of the unit.

8. The prosthesis of claim 1 in which the circuitry includes limit switches operable at either of the limits to which the second member may swing to open said circuitry.

9. The prosthesis of claim 1 in which the circuitry including its power source is housed within the second member.

10. The prosthesis of claim 1 in which the first stage of the transmission includes an internally toothed ring gear, a gear fast on the motor drive shaft, and a rotatable member includes planetary gears in mesh with said ring and drive shaft gears, and the clutch includes a housing and a driven member, means connecting the housing and the ring gear to the motor casing and a driving connection between the rotatable member and the driven member of the clutch.

11. The prosthesis of claim 10 in which the driven member of the clutch includes an output cam having oppositely disposed parallel flats and a shaft, the rotatable member includes oppositely disposed spaced pairs of connectors, the pairs receiving said flats freely between them to provide said driving connection when the motor is in operation, and rollers confined freely between the connectors of each pair but permitting them to become jammed between the clutch housing and the flats when said second member is moved in one direction when the motor is not driving said second member in that direction.

12. The prosthesis of claim 11 in which said one direction is the joint-straightening direction.

13. The prosthesis of claim 11 in which the clutch housing includes a flange and an outer clutch housing clamps said flange against the face of the ring gear to an extent providing frictional resistance against the flange turning in either direction.

14. The prosthesis of claim 11 in which the second stage is a transmission of the plano-centric type with its driven shaft the output shaft of the unit, the second stage including a fixed circular spline, the motor, the first stage including a fixed circular spline, the motor, the first stage and the clutch are housed within the second stage and the motor is connected thereto to rotate therewith. and the fixed circular spline of the second stage is fixed within the unit. 15. The prosthesis of claim 11 and a DC PM tachometer coupled to the motor and operable to provide a signal proportional to the rate of flexing velocity so that when the rotatable member unjams the rollers and the external load on the arm causes the output cam to go in the same direction the feedback signal prevents the arm from taking off in a mannor not intended by the amputee.

16. The prosthesis of claim 11 in which the acute angle which a line perpendicular to the face of each flat of the output cam and which passes through the center of the appropriate roller would make with a second line also passing through the center of the roller and through the point of its tangency to the inside of the housing is no less than l2.14 and no more than 15. 14 in order to minimize the force required by the rotatable member to unjam the rollers.

17. The prosthesis ofclaim 4 and a deadband following the signal-combining summer providing the difference signals to bar extraneous EMG signals, said deadband being in the neighborhood of ten percent of the maximum signal level.

18. The prosthesis ofclaim 17 in which the deadband motor driving amplifier, a triangular wave generator to provide the amplitude of the pulses and having a signal excursion extending from 0 volts to a positive level,

said zero level comprising first and second resistors and a diode, said first resistor comprising the second deadband and biasing said zero point to a positive value that eliminates voltage in the neighborhood of ten percent of the voltage output of said generator.

21. The prosthesis ofclaim 4 in which the pulse modulating and motor driving amplifier includes two pairs of power transistors, each pair for a particular polarity of the pulse delivered thereto, and a flip-flop operable to select the appropriate pair of power transistors that is to be operated to control direction in response to the polarity of the polarity signals and shiftable only on and at the leading edge of the pulse width modulation pulse.

Claims (21)

1. A prosthesis comprising a first member having a stump receiving socket and provided with a support at its distal end, a second member, a joint unit secured to the support of the first member, a pivotal connection between said joint unit and the second member relative to said first member, a drive including a direct current permanent magnet motor and a transmission housed within the unit with the output shaft of the transmission so connected to said second member that said second member is flexed relative to said first member in a direction dependent on the direction in which said motor is operating, said transmission including first and second reduction stages and a reverse locking clutch between said stages operable under the conditions that the second member is in support of a load and the motor is not operating to move the member to raise or lower the load and electric circuitry including said motor, a battery, electrodes attachable to the stump and operable to detect EMG signals from the stump muscles that were used to flex and straighten the amputee''s missing joint, and signal processing means operable to convert the detected signals into signals that operate the motor in the direction and rate that corresponds to the strength of the dominant EMG signals.

2. The prosthesis of claim 1 in which the first stage is a planetary gear reduction unit and the second stage is a plano-centric drive.

3. The prosthesis of claim 1 in which the transmission also includes a friction brake that may slip to provide a cushion and the engagement of the reverse locking clutch.

4. The prosthesis of claim 1 and a direct current permanent magnet tachometer coupled to the motor and operable to provide a signal proportional to the rate at which said second member moves relative to the first member, the signal processing means includes means to amplify and convert the signals indicative of flexing to one polarity and those indicative of straightening to the other polarity, a summer operable to combine said signals to provide a difference signal, the tachometer provides a feedback signal proportional to the rate of flexing velocity, means summing the feedback and the difference signals to decrease the power input when said rate is greater than that intended by the wearer of the prosthesis, and a pulse width modulation and motor driving amplifier in which battery circuit determines the amplitude of the pulses.

5. The prosthesis of claim 4 in which the reverse locking clutch includes a friction brake operable, when a load is beiNg lowered to cushion by slipping the reengagement of the clutch as the motor and the load alternatively release and lock the clutch.

6. The prosthesis of claim 1 in which the circuitry includes deadband means operable to exclude substantially all extraneous signals that would, when zero movement of the second member was wanted, cause battery drain.

7. The prosthesis of claim 6 in which the value of the deadband means is less than the mechaical deadband created by friction of the unit.

8. The prosthesis of claim 1 in which the circuitry includes limit switches operable at either of the limits to which the second member may swing to open said circuitry.

9. The prosthesis of claim 1 in which the circuitry including its power source is housed within the second member.

10. The prosthesis of claim 1 in which the first stage of the transmission includes an internally toothed ring gear, a gear fast on the motor drive shaft, and a rotatable member includes planetary gears in mesh with said ring and drive shaft gears, and the clutch includes a housing and a driven member, means connecting the housing and the ring gear to the motor casing and a driving connection between the rotatable member and the driven member of the clutch.

11. The prosthesis of claim 10 in which the driven member of the clutch includes an output cam having oppositely disposed parallel flats and a shaft, the rotatable member includes oppositely disposed spaced pairs of connectors, the pairs receiving said flats freely between them to provide said driving connection when the motor is in operation, and rollers confined freely between the connectors of each pair but permitting them to become jammed between the clutch housing and the flats when said second member is moved in one direction when the motor is not driving said second member in that direction.

12. The prosthesis of claim 11 in which said one direction is the joint-straightening direction.

13. The prosthesis of claim 11 in which the clutch housing includes a flange and an outer clutch housing clamps said flange against the face of the ring gear to an extent providing frictional resistance against the flange turning in either direction.

14. The prosthesis of claim 11 in which the second stage is a transmission of the plano-centric type with its driven shaft the output shaft of the unit, the second stage including a fixed circular spline, the motor, the first stage including a fixed circular spline, the motor, the first stage and the clutch are housed within the second stage and the motor is connected thereto to rotate therewith, and the fixed circular spline of the second stage is fixed within the unit.

15. The prosthesis of claim 11 and a DC PM tachometer coupled to the motor and operable to provide a signal proportional to the rate of flexing velocity so that when the rotatable member unjams the rollers and the external load on the arm causes the output cam to go in the same direction the feedback signal prevents the arm from ''''taking off'''' in a mannor not intended by the amputee.

16. The prosthesis of claim 11 in which the acute angle which a line perpendicular to the face of each flat of the output cam and which passes through the center of the appropriate roller would make with a second line also passing through the center of the roller and through the point of its tangency to the inside of the housing is no less than 12.14* and no more than 15.14* in order to minimize the force required by the rotatable member to unjam the rollers.

17. The prosthesis of claim 4 and a deadband following the signal-combining summer providing the difference signals to bar extraneous EMG signals, said deadband being in the neighborhood of ten percent of the maximum signal level.

18. The prosthesis of claim 17 in which the deadband comprises parallel opposite diodes in front of the means summing velocity feedback signals and the EMG difference signals.

19. The prosthesis of claim 17 anD a second deadband to eliminate DC drift and noise incidental to the second summing, said second deadband being incorporated in the circuitry before the pulse width modulating and motor driving amplifier and being in the neighborhood of ten percent of the maximum signal level.

20. The prosthesis of claim 19 in which the circuitry includes as part of the pulse width modulating and motor driving amplifier, a triangular wave generator to provide the amplitude of the pulses and having a signal excursion extending from 0 volts to a positive level, said zero level comprising first and second resistors and a diode, said first resistor comprising the second deadband and biasing said zero point to a positive value that eliminates voltage in the neighborhood of ten percent of the voltage output of said generator.

21. The prosthesis of claim 4 in which the pulse modulating and motor driving amplifier includes two pairs of power transistors, each pair for a particular polarity of the pulse delivered thereto, and a flip-flop operable to select the appropriate pair of power transistors that is to be operated to control direction in response to the polarity of the polarity signals and shiftable only on and at the leading edge of the pulse width modulation pulse.

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