Bioelectrically controlled prosthetic member

• US 3,883,900 A
• Filed: 09/07/1973
• Issued: 05/20/1975
• Est. Priority Date: 09/07/1973
• Status: Expired due to Term

• Current Assignee: Cord W. Ohlenbusch, Robert B. Jerard
• Original Assignee: Cord W. Ohlenbusch, Robert B. Jerard
• Inventors: Jerard, Robert B., Ohlenbusch, Cord W.
• Primary Examiner(s): Frinks, Ronald L.
• Application Number:
  US05/395,236
• Time in Patent Office: 620 Days
• Field of Search: 3/1.1,12-12.3
• US Class Current: 623/25
• CPC Class Codes: A61F 2/58 Elbows; Wrists ; Other joints; Hands
• CPC Class Codes: A61F 2/72 Bioelectric control, e.g. myoelectric
• CPC Class Codes: A61F 2002/30523 by means of meshing gear teeth
• CPC Class Codes: A61F 2002/701 operated by electrically controlled means, e.g. solenoids or torque motors
• CPC Class Codes: A61F 2220/0025 Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements

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.

Claims

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.