Myoelectrically controlled knee joint locking device

A damped knee joint may be locked myoelectrically at any angle of flexing. A special hydraulic cylinder is pivoted above the knee center at one end and in the shank at the other end. This attachment strategy allows 110 degrees of knee flexion, permitting the normal range of sitting and standing positions. The cylinder assembly incorporates a closed loop, sealed hydraulic system and electro-mechanical valving to control piston position. The closed loop hydraulic system also prevents fluid leakage and contamination. Valving is accomplished by a microelectrically operated barrel or gate valve located in a hydraulic system. The use of a barrel or gate valve allows the microelectrically operated plunger to be physically isolated from the working fluid and to be operated reliably at the highest working pressure of the systems.

FIELD OF THE INVENTION 
This invention relates to a myoelectrically controlled device for locking 
of a knee joint upon detection of uncontrolled flexion and/or falling. 
BACKGROUND OF THE INVENTION 
There is an urgent need for an above knee (AK) amputee's ability to control 
above knee prosthesis, regardless of age or physical condition, e.g. 
second world war veterans and geriatrics. The demand exists for an active, 
volitionally controlled above knee prosthesis. Current prosthesis are 
passive devices that are awkward, and the amputee has little or no 
control. 
The basic problem involved with existing limbs is that while unilateral AK 
amputees routinely "flex" the prosthesis limb while walking, bilateral 
amputees most often walk with one or both knees locked to provide 
stability. The use of passive locks makes sitting, at best, difficult. 
Current knee units for a patient's use include a mechanical locking system 
located at the knee joint. The amputee must reach down and disengage the 
lock while braced against a suitable support and then lower himself into a 
sitting position. The difficulty is such that the amputee only unlocks the 
lock when sitting down, while unlocked knees would also be optimal for 
walking on a level surface. The limitations of the conventional knee 
system are further demonstrated by the amputee's inability to traverse 
even the smallest of grades. 
Previous attempts to provide myoelectrically controlled prosthetic devices 
are described in U.S. Pat. No. 3,631,542 to Potter, U.S. Pat. No. 
3,501,776 to Beeker et al., U.S. Pat. No. 4,623,354 to Childress et al. 
and U.S. Pat. No. 4,314,379 to Tanie et al. 
Additionally, many patents are directed to hydraulic devices for control of 
prosthesis movement. Some of these patents are U.S. Pat. Nos. 3,799,159 to 
Scott, 3,670,341 to Webb et al., 4,065,815 to Sen-Jung, 4,051,558 to 
Vallotton, 3,995,324 to Burch, 3,871,032 to Karas, 3,800,333 to Friberg, 
4,212,087 to Mortensen, 4,662,486 to Stenberg, 4,578,082 to Sen-Jung and 
4,775,037 to Stenberg. 
SUMMARY OF THE INVENTION 
The present invention eliminates all of the preceding problems and 
limitations and is a solution available to AK amputees between what is 
available now and the ultimate, although somewhat futuristic, bionic 
solution. 
The present invention involves the amputee's active control of the 
prostheses, like the ability to respond to events, such as standing, 
walking on unlevel surfaces, stumble recovery, going up and down stairs, 
getting in and out of a chair, or simply walking up or down a curb. This 
control does not only decrease metabolic energy expenditure, but also 
reduces the resultant stress factor (fatigue). In other words, the control 
unit overcomes most limitations of any other known conventional knee 
system. Minimal training, regardless of the amputee's age or physical 
condition, is required to proficiently operate the control unit. 
By the present invention, a controlled damped knee joint may be locked 
myoelectrically at any angle of flexing. This unit is a substantial 
improvement over non-controllable units on the market today designed for 
above-knee amputees. The inventive system uses a special hydraulic 
cylinder, pivoted above the knee center at one end and in the shank at the 
other end. This attachment strategy allows 110 degrees of knee flexion, 
permitting the normal range of sitting and standing positions. 
The cylinder assembly incorporates a closed loop, sealed hydraulic system 
and electro-mechanical valving to control piston position. The closed loop 
hydraulic system also prevents fluid leakage and contamination. 
Valving is accomplished by a microelectrically operated barrel or gate 
valve located in a hydraulic system. The use of a barrel or gate valve 
allows the microelectrically operated plunger to be physically isolated 
from the working fluid and to be operated reliably at the systems highest 
working pressure. 
The system is fitted with a lock out plunger valve which allows the piston, 
i.e. knee, to remain locked and still allow the operator (amputee) to move 
the leg into full extension, maintaining control of the lower extremity of 
the prostheses. 
Solenoid actuation is accomplished through myoelectric control by 
monitoring a muscle site providing a myoelectrical signal. The strategic 
placement of the receiver eliminates the possibility of outside signal 
interference. 
An optimum site is chosen over a muscle that responds reflexively to 
imbalance, flexion and falling. Regardless of any other signal, the 
optimal signal will instantly lock the knee joint at any angle. 
The hydraulic electronic limb prosthesis unit, which may be retrofitted to 
existing artificial limbs in addition to being an integral component in 
the manufacturing of new artificial limbs, consists of an electronically 
operated and user controlled, multiple-logic closed loop hydraulic 
circuit. 
The locking device includes a specially designed hydraulic cylinder with an 
internal sponge accumulator which provides improved, smooth fluid 
displacement. A cartridge-designed flow valve with built-in internal check 
valve provides a wide range of limb extension velocity adjustments on an 
independent basis. A separate cartridge-designed flow control valve with 
built-in internal check value, provides a wide range of limb flexing 
(retraction) velocity adjustments on an independent basis. 
A two-way, electrically operated solenoid control valve includes a 
specially-designed spool. When de-activated, the control valve provides 
open hydraulic fluid flow for user controlled extension or flexing 
(retraction) movements. When activated, the control valve provides a check 
valve controlled hydraulic fluid flow for automatically inhibiting of 
flexing (retraction) movement and an open hydraulic fluid flow for user 
control of extension movement only. The control valve is electronically 
controlled, in a logic-manner (off - deactivated, on - activated) by the 
myoelectronic and buffer amplifier modules. 
The myoelectronic unit is activated by electronic detection of specified 
muscle movement as a result of an involuntary movement, such as an 
unexpected imbalance or reflex reaction to initiation of a fall. A signal 
generated by the myoelectronic unit activates the control valve, by means 
of the buffer amplifier, to automatically inhibit flexing (retraction) 
movement by blockage of fluid flow in one direction but automatically 
allows the user control of extension movement by allowing continued fluid 
flow in an opposite direction. This provides a tremendous safety 
advantage. 
Also, the user may utilize detection of specified muscle contraction as a 
result of voluntary movement to provide the automatic inhibit of flexing 
(retraction) movement control and user control for extension movement to 
provide the capability of ascending and descending inclines, street curbs 
and steps. This provides a tremendous mobility advantage. 
The myoelectronic module of the invention detects specified muscle 
contraction and upon activation, provides a low power voltage signal to a 
buffer amplifier. This activated signal is the logic-control for a 
two-way, electronically operated solenoid control valve of a 
piston-cylinder unit for controlled activation and deactivation of the 
extension and flexing (retraction) of limb prosthesis movement. The buffer 
amplifier, which accepts the low power voltage signal from the 
myoelectronic unit, provides a voltage to current amplification power 
necessary to activate the two-way, electrically operated solenoid control 
valve for automatic activation. 
A portable, rechargeable Ni-Cad battery pack is utilized to provide 
adequate electrical power for system operation. The battery pack also 
includes a low power level annunciator. If the battery pack is not 
sufficiently charged, the user may utilize the hydraulic electronic limb 
prosthesis unit in a conventional manner without the flexing inhibitor. 
It is therefore an object of the present invention to provide a 
myoelectrically controlled knee joint locking device for controlling a 
hydraulic piston cylinder assembly for locking of the knee joint against 
retraction movement upon transmission of a myoelectric signal. 
It is yet another object of the present invention to provide a 
myoelectrically controlled knee joint locking device for controlling a 
hydraulic piston cylinder assembly for locking of the knee joint against 
retraction movement upon transmission of a myoelectric signal with 
independently controlled hydraulic fluid velocity adjustment for 
controlled extension and retraction of the knee joint. 
It is yet another object of the present invention to provide a 
myoelectrically controlled knee joint locking device for controlling a 
hydraulic piston cylinder assembly for locking of the knee joint against 
retraction movement upon transmission of a myoelectric signal with 
independently controlled hydraulic fluid velocity adjustment for 
controlled extension and retraction of the knee joint, with a 
myoelectrically controlled solenoid actuated to prevent retraction of the 
knee joint. 
These and other objects of the invention, as well as many of the intended 
advantages thereof, will become more readily apparent when reference is 
made to the following description taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In describing a preferred embodiment of the invention illustrated in the 
drawings, specific terminology will be resorted to for the sake of 
clarity; however, the invention is not intended to be limited to the 
specific terms so selected, and it is to be understood that each specific 
term includes all technical equivalents which operate in a similar manner 
to accomplish a similar purpose. 
With reference to the drawings, in general, and to FIG. 1, in particular, a 
myoelectrically controlled knee joint locking device embodying the 
teachings of the subject invention is generally designated as 10. With 
reference to FIG. 1, the myoelectrically controlled knee joint locking 
device includes a lower artificial limb 12 pivotably mounted on an upper 
artificial limb 14 having an artificial limb attachment socket 16. 
A hydraulic piston cylinder unit 18 interconnects the lower artificial limb 
12 and the upper artificial limb 14. One end 20 of the cylinder 22 is 
pivotally mounted by lower anchor/pivot point 24 to the lower artificial 
limb 12. One end 26 of piston rod 28 is connected to an upper anchor/pivot 
point 30 on the upper artificial limb 14. 
By extension and retraction of the piston rod 28, the upper and lower 
artificial limbs 12 and 14 are moved with respect to each other. The 
movement of the upper and lower artificial limbs 12 and 14 is controlled 
by a limb of an above knee amputee inserted into the artificial limb 
attachment socket 16. 
A myoelectronic unit 32 is located on a responsive muscle of the amputee 
for detection of myoelectric potential which is an electrical potential 
created by muscle action. The sensor unit 32 transmits an electrical 
signal across signal wire 34 to a myoelectronic control unit 36. The 
myoelectronic sensor unit 32 and the myoelectronic control unit 36 are 
powered by battery pack 38. Power wire 40 is connected between the battery 
pack 38 and myoelectronic sensor unit 32. 
A signal received by the myoelectronic control unit 36 is amplified and 
transmitted by solenoid power wires 42 to piston cylinder unit 18, housing 
a solenoid therein. By actuation of the solenoid, hydraulic fluid flow in 
the piston cylinder unit is only allowed to flow for extension of the 
lower artificial limb 12. Any retraction of the artificial limb 12 is 
prevented by blockage of a path of hydraulic fluid flow used for the 
retraction of the lower artificial limb with respect to the upper 
artificial limb. 
In FIG. 2, a sectional view of the piston cylinder unit 18 is shown. With 
reference to the upper and lower artificial limbs shown in FIG. 1, upon 
extension of the lower artificial limb, as in taking a step forward, the 
piston 44 moves to the right in the direction of arrow A of FIG. 2. With 
reference to FIG. 2, during the extension of the lower artificial limb, 
the piston rod 28 moves out of the rod end cylinder cap cover 46, again in 
the direction of arrow A. 
During extension of the lower artificial limb, hydraulic fluid in reservoir 
84 on the right side of the piston 44, enters a return flow path (however 
not shown in FIG. 2 for clarity of the drawing) for the hydraulic fluid to 
pass around the piston 44 and return to the left side of the piston 44, to 
reservoir 85, when the plunger moves in the direction of arrow A. A seal 
52 in the rod end cylinder cap cover 46 prevents leakage of fluid around 
the piston rod 28. 
When the lower artificial limb 12 is bent rearwardly for retraction of the 
lower artificial limb, the piston 44 is moved in the direction of arrow B, 
towards the left side of FIG. 2. As the piston approaches the intermediate 
section cylinder cap 54, fluid is forced into opening 56 of tube 60 
surrounded by 0-ring 58. Tube 60 includes lateral hole 62 which empties 
fluid passing through the tube 60 into passage 64 defined in cylinder cap 
54. A bypass passage tube 66 is connected to passage 64 to continue 
transfer of hydraulic fluid from the reservoir 85 on the left side of 
piston 44, during retraction of lower artificial limb 12. 
From tube 66, fluid is moved into passage 68 defined by cap cover 46. A 
check valve 70 includes a ball 72 and biased spring 74 which allows 
passage of fluid in a single direction by forcing the ball 72 against the 
spring 74. Passage of fluid in an opposite direction is prevented by the 
bias of the spring 74 forcing ball 72 to block access to passage 66. A 
threaded needle flow control valve 76 is threaded into cap cover 46 to 
vary the size of the passage 78 so as to control the amount of fluid 
passing thereby and thus control the speed of movement of the retraction 
of the lower artificial limb 12 towards the upper artificial limb 14. 
Fluid passing through passage 78 continues through angled passageway 80 
and into annular space 82 defined around piston rod 28 for passage of 
hydraulic fluid to the reservoir 84 on the right side of the piston 44. 
As schematically shown in FIG. 3, passage of hydraulic fluid in the 
direction of arrows of A and B is permitted dependent upon the control of 
the speed of the flow by two separate needle flow control valves. The flow 
control valves are located in two separate passageways, as schematically 
represented in FIG. 3 by extension adjustment 86 including a check valve 
and a flow control valve for extension of lower artificial limb 12 and 
retraction adjustment 88 including check valve 72, 74 and flow control 
valve 76 for retraction adjustment of lower artificial limb 12. 
Extension adjustment 86 and retraction adjustment 88 are schematic 
representations of the two actual flow paths for fluid to bypass piston 44 
by passageways 90, 91 and 92. The direction of flow through passages 90, 
91 and 92 is dependent upon the direction of movement of the lower 
artificial limb, either extending or retracting. The two check valves 
forming part of the retraction adjustment and extension adjustment 86 and 
88 limit the direction of flow of fluid to a single direction of flow. 
When a myoelectronic signal is generated by myoelectronic sensor unit 32 as 
a result of a detection of a myoelectric potential in the muscle of the 
user, the signal is transmitted by signal wire 34 to myoelectronic control 
unit 36. The signal is amplified and then transmitted by solenoid power 
wires 42 to hydraulic solenoid valve 94. Hydraulic solenoid valve 94 
includes a plunger 96 having a spool 98 at one end. Upon receipt of a 
signal by the hydraulic solenoid valve, the solenoid valve is activated so 
that the plunger 96 is extended to move the spool 98 to block passage of 
fluid through the hole 62 of tube 60 to thereby provide a directional 
control of fluid flow. The blockage of the hole 62 prevents any further 
movement of the plunger 44 in the direction of arrow B and thereby 
prevents any further retraction of the lower artificial limb 12. 
Therefore, upon receipt of a myoelectric signal generated by a muscle, 
indicative of unexpected imbalance or beginning of a fall, the knee joint 
is immediately locked in position and any further retraction of the lower 
artificial limb is prevented. 
Upon sensing of the locked knee joint by the amputee, the amputee is then 
able to exert pressure on the upper and lower artificial limbs to cause 
extension of the lower artificial limb so as to regain balance and prevent 
a fall. The extension of the lower artificial limb is possible because 
even in the actuated state of the hydraulic solenoid valve 94, the piston 
44 is allowed to move in the direction of arrow A for extension of the 
lower artificial limb by forcing hydraulic fluid in reservoir 84 into 
sponge accumulator 48 through openings 50. Sponge accumulator 48 is of an 
annular configuration, encircling the piston rod 28. 
In FIG. 4, an exploded view of the hydraulic piston cylinder assembly is 
shown. The elements in common with those shown in FIG. 2 are similarly 
numbered. In addition, in FIG. 4, tie rods 100 are shown, it being 
understood that eight (8) tie rods are included for connecting rod end 
cylinder cap 46 with intermediate section cylinder cap 54 and cylinder cap 
102. The hydraulic solenoid valve 94 is housed within a cylinder tube 104. 
Solenoid wires 42 extend through the cylinder cap 102 to the solenoid 
control valve 94. 
A piston seal 106 surrounds piston rod 44. Similarly, tube end seals 108 
are located on the opposite ends of cylinder 22 to seal the ends of the 
cylinder tube 22 that is subject to hydraulic fluid pressure. 
In FIG. 4, only one assembly of check valve and flow control valve 72, 74, 
76 is shown, these components forming retraction adjustment 88 for 
retraction of the lower artificial limb 12. It being understood, as shown 
in FIG. 3, that a similar assembly is defined between rod end cylinder cap 
46 and intermediate section cylinder cap 54 for flow of hydraulic fluid 
for extension movement of lower artificial limb 12 to bypass piston 44, 
with a similar check valve which prevents flow of fluid in one direction 
as represented by extension adjustment 86 in FIG. 3. 
In FIG. 5, a schematic electrical diagram of the circuitry of the present 
invention is shown. The myoelectronic sensor unit 32 is a myobock 
electrode available from Otto Bock Orthopaedic, Inc., part number 13E67 
for electronic detection of specified muscle movement. The sensor provides 
a +6 volt d.c. low current signal to an input of an operational amplifier 
IC1 by signal wire 34. 
The sensor unit 32 is powered by a +12 volt d.c. battery pack 38 with a +6 
volt d.c. supply voltage from a nickel cadmium rechargeable-type battery. 
A standard female plug-in receptacle 112 for battery pack accessories 
provides a plug-in interface from a battery charger unit to the battery 
pack. Battery charger unit 114 includes a standard male plug-in connector 
from a battery charger unit. A standard UL approved 115 volt a.c. source 
provides a charge to the battery pack 38. 
Resistor 116 (R.sub.1) is a 1M.OMEGA., 1/8 watt, 1% tolerance resistor to 
provide electronic impedance from the myoelectronic sensor 32 to an IC1 
operational amplifier circuit 120. 
Resistor 118 (R.sub.2) is a 3K.OMEGA., 1/4 watt, 1% tolerance resistor 
which is an electronic bias control for operation of the IC1 operational 
amplifier circuit 120. 
Operational amplifier 120 is available from Linear Technology, part number 
LT1010CT, which provides current amplification from the myoelectronic 
sensor (approximately 0.08a) to operate the transistor (Q1) (approximately 
30 ma). 
Resistor 122 (R.sub.3) is a 330.OMEGA., 1/2 watt, 1% tolerance resistor to 
provide electronic bias control for operation of transistor Q1 (type NPN, 
2N2219A). 
Transistor 124 (Q.sub.1) (type NPN, 2N2219A) provides voltage and current 
amplification from the operational amplifier (6 volt d.c. @ 30 ma) to 
operate the control valve solenoid 94 (12 volt d.c. @ 250 ma). 
Diode 126 (D.sub.1) (1N3600) is a clamping diode to protect transistor 124 
(Q.sub.1) (2N2219A) from negative voltage generated when the coil of the 
solenoid control valve 94 is de-energized. 
Two-way electrically operated solenoid control valve 94 with specially 
designed spool arrangement 98 is activated upon generation of a signal by 
myoelectronic sensor unit 32. 
By the present invention, independent control of the adjustment for 
retraction and extension of an upper and lower portion of an artificial 
limb is made possible for an above knee amputee. In addition, upon 
generation of a reflexive myoelectric signal indicative of imbalance, 
retraction of a hydraulic piston unit interposed between an upper and 
lower portion of an artificial limb is prevented and only extension of the 
artificial leg is permitted. The generation of the myoelectric signal may 
be intentionally controlled by the amputee to assist in ascending and 
descending inclines, curbs and steps. 
Having described the invention, many modifications thereto will become 
apparent to those skilled in the art to which it pertains without 
deviation from the spirit of the invention as defined by the scope of the 
appended claims.