Method and apparatus for switching degrees of freedom in a prosthetic limb

• US 5,336,269 A
• Filed: 06/09/1992
• Issued: 08/09/1994
• Est. Priority Date: 06/09/1992
• Status: Expired due to Fees

• Current Assignee: Liberating Technologies, Inc.
• Original Assignee: Liberty Mutual Insurance Company (Liberty Mutual Holding Company)
• Inventors: Smits, Matthijs P.
• Primary Examiner(s): Green, Randall L.
• Assistant Examiner(s): WILLSE, DAVID H
• Application Number:
  US07/896,058
• Time in Patent Office: 791 Days
• Field of Search: 623/25, 623/57, 623/64, 623/24, 128/733
• US Class Current: 623/25
• CPC Class Codes: A61F 2/582 Elbow joints
• CPC Class Codes: A61F 2/72 Bioelectric control, e.g. myoelectric

Abstract

The invention comprises a method and apparatus for switching between degrees of freedom in a prosthesis responsive to myoelectric signals generated by muscles. In the invention, an average pattern corresponding to a specified muscle contraction is stored in memory. In operation, the invention continuously stores a specified preceding interval of the incoming myoelectric signals and compares the data in that interval with the stored average pattern. If the incoming data is sufficiently similar to the stored average pattern, a recognition occurs and the device switches degrees of freedom.

Claims

1. A method for switching amongst a plurality of degrees of freedom of a prosthesis comprising the steps of;

(1) storing a pattern representing myoelectric signals of a muscle corresponding to a predesignated muscle contraction, said pattern comprising a first plurality of data points, each data point being representative of an instantaneous amplitude of said myoelectric signals at an instant in time,

(2) obtaining a second plurality of data points, each of said second plurality of data points being representative of the instantaneous amplitude of myoelectric signals of said muscle in real time,

(3) comparing said second set of data points with said first set of data points, and

(4) switching amongst said degrees of freedom if said real time myoelectric signals are similar to said stored pattern within a predetermined limit.

2. A method as set forth in claim 1 wherein step (1) further comprises the sub-steps of;

(1.1) causing said predesignated muscle contraction to be performed at least one time,

(1.2) receiving said myoelectric signals corresponding to said movement,

(1.3) full wave rectifying said myoelectric signals,

(1.4) smoothing said myoelectric signals corresponding to said movement,

(1.5) converting said myoelectric signals corresponding to said movement to digital data, and

(1.6) storing said digital data in memory as said first plurality of data points.

3. A method as set forth in claim 2 wherein said muscle is a pair of agonist-antagonist muscles.

4. A method as set forth in claim 2 wherein step (1) further comprises the sub-steps of;

(1.55) repeating steps (1.1) through (1.5) a plurality of times in order to obtain a plurality of patterns, and

(1.56) determining an average pattern based on said plurality of patterns generated, said first plurality of data points comprising said average pattern.

5. A method as set forth in claim 4 wherein step (2) further comprises the sub-steps of;

(2.1) receiving said real time myoelectric signals,

(2.2) smoothing said real time myoelectric signals, and

(2.3) converting said real time myoelectric signals to digital data.

6. A method as set forth in claim 5 wherein step (1) further comprises the sub-steps of;

(1.8) determining the deviation of each of said plurality of patterns from said average pattern,

(1.9) determining said pattern having a maximum deviation from said average pattern, and

(1.10) storing said maximum deviation.

7. A method as set forth in claim 6 wherein step (3) comprises;

(3.1) determining the deviation of said second plurality of data points from said first plurality of data points.

8. A method as set forth in claim 7 wherein step (4) comprises;

(4.1) switching degrees of freedom only if said deviation of said second plurality of data points from said first plurality of data points is less than or equal to said stored maximum deviation.

9. A method as set forth in claim 8 wherein said prosthesis has at least first and second degrees of freedom, said prosthesis at any given time being in a first mode in which it controls said first degree of freedom or in a second mode in which it controls said second degree of freedom and wherein step (4.1) further comprises the step of;

(4.1.1) if said prosthesis is in said first mode, switching to said second mode, and if said prosthesis is in said second mode, switching to said first mode.

10. A method as set forth in claim 9 further comprising the step of;

(1.2.1) amplifying said myoelectric signal.

11. A method as set forth in claim 10 further comprising the step of (1.2.05) filtering noise out of said myoelectric signal.

12. A method as set forth in claim 11 wherein said predesignated muscle contraction is a fast muscle contraction.

13. A method as set forth in claim 12 wherein said stored pattern comprises approximately 300 milliseconds of data and wherein steps (1.4) and (2.2) comprise smoothing so as to eliminate frequency components above approximately 10 Hz and steps (1.5) and (2.3) comprise converting at a rate of 50 Hz.

14. A method as set forth in claim 13 wherein said plurality of times referred to in step (1.6) comprises approximately 10 times.

26. A method as set forth in claim 3 wherein said muscle is a pair of agonist-antagonist muscles.

15. An apparatus for switching amongst a plurality of degrees of freedom of a prosthesis comprising;

memory means for storing a a first plurality of data points corresponding to myoelectric signals generated by a muscle corresponding to a predesignated muscle contraction, each data point being representative of an instantaneous amplitude of said myoelectric signals corresponding to said predesignated muscle contraction,

means for receiving myoelectric signals from said muscle,

means for converting said myoelectric signals to a second plurality of data points, each data point being representative of an instantaneous amplitude of said received myoelectric signal,

processing means for comparing said second plurality of data points with said first plurality of data points, and

means for switching degrees of freedom of said prosthesis responsive to said second plurality of data points being similar to said first plurality of data points within a specified tolerance.

16. An apparatus as set forth in claim 15 wherein said first plurality of data points comprises myoelectric signals generated by first and second muscles, respectively, of a pair of agonist-antagonist muscles, and wherein said means for receiving myoelectric signals comprises first means for receiving first myoelectric signals from said first muscle and second means for receiving second myoelectric signals from said second muscle.

17. An apparatus as set forth in claim 16 wherein;

said converting means converts said myoelectric signals to digital data at a specified rate corresponding to the data of said first plurality of data points, and said processing means comprises;

means for continuously storing, as said second plurality of data points, data points corresponding to a specified interval of the immediately preceding first and second myoelectric signals, and

means for comparing said data points of said stored specified interval of said immediately preceding first and second myoelectric signals with said first plurality of data points each time a pair of data points is converted.

18. An apparatus as set forth in claim 17 wherein said means for receiving said first myoelectric signals and said means for receiving said second myoelectric signals each comprise;

a twin-contact electrode placed on a skin surface adjacent to the respective muscle,

an amplifier for amplifying said myoelectric signals,

a filter for removing noise from said myoelectric signals,

a full-wave rectifier,

a smoothing circuit for smoothing said myoelectric signal, and

wherein said means for converting comprises an analog-to-digital converter.

19. An apparatus as set forth in claim 18 wherein,

said processing means further comprises means for determining the deviation of said second plurality of data points from said first plurality of data points, and

said means for switching is responsive to said deviation for switching degrees of freedom when said deviation is less than a specified value.

20. An apparatus as set forth in claim 19 wherein said prosthesis has at least first and second degrees of freedom, said prosthesis at any given time being in a first mode in which it controls said first degree of freedom or in a second mode in which it controls said second degree of freedom and wherein said switching means comprises;

means for switching said prosthesis to said second mode, if said prosthesis is in said first mode, and means for switching said prosthesis to said first mode, if said prosthesis is in said second mode.

21. An apparatus as set forth in claim 20 wherein said predesignated muscle contraction is a fast muscle contraction.

22. An apparatus as set forth in claim 21 wherein said first plurality of data points and said second plurality of data points each comprise approximately 300 milliseconds of digital data sampled at a rate of approximately 50 Hz.

23. An apparatus as set forth in claim 22 further comprising means for obtaining said first plurality of data points, said means comprising;

means for obtaining a plurality of patterns of said myoelectric signals from said first and second muscles corresponding to a plurality of said predesignated muscle contractions,

means for determining said first plurality of data points by determining the average value for each data point of said plurality of patterns,

means for determining the deviation of each of said plurality of patterns from said average values,

means for determining which one of said plurality of patterns has a maximum deviation from said average pattern, and

means for storing said average pattern at said first set of data points and said maximum deviation, said maximum deviation comprising said specified threshold.

24. An apparatus for switching amongst a plurality of degrees of freedom of a prosthesis comprising;

a digital memory for storing a first plurality of data points corresponding to first and second myoelectric signals generated by first and second muscles, respectively, of a pair of agonist-antagonist muscles corresponding to a predesignated muscle contraction, each data point being representative of an instantaneous amplitude of said myoelectric signals at an instant in time,

a first electrode for receiving first myoelectric signals from said first electrode,

a second electrode for receiving second myoelectric signals from said second muscle,

a rectifier for full-wave rectifying said first and second myoelectric signals,

a smoothing circuit for smoothing said first and second myoelectric signals,

an analog-to-digital converter for converting said first and second myoelectric signals to a second plurality of data points, each of said second plurality of data points being representative of an instantaneous amplitude of said first or second myoelectric signals, respectively,

processing means for comparing said second plurality of data points with said first plurality of data points, and

a switch for switching degrees of freedom of said prosthesis responsive to said second plurality of data points being similar to said first plurality of data points within a specified tolerance.

25. An apparatus for switching amongst a plurality of degrees of freedom of a prosthesis comprising;

a digital memory for storing a first set of data points corresponding to first and second myoelectric signals generated by first and second muscles, respectively, of a pair of agonist-antagonist muscles corresponding to a predesignated muscle contraction, each data point being representative of an instantaneous amplitude of said myoelectric signals at an instant in time,

a first twin-contact electrode for receiving first myoelectric signals from said first muscle,

a second twin-contact electrode for receiving second myoelectric signals from said second muscle,

a third electrode for receiving a ground reference signal,

an amplifier for amplifying said first and second myoelectric signals,

a filter for removing noise from said first and second myoelectric signals,

a rectifier for full-wave rectifying said first and second myoelectric signals,

a smoothing circuit for smoothing said first and second myoelectric signals,

an analog to digital converter for converting said first and second myoelectric signals to a second plurality of data points, each of said second plurality of data points being representative of an instantaneous amplitude of said first or second myoelectric signals, at a specified rate corresponding to the data on said first set of data points,

processing means comprising,

means for continuously storing, as said second plurality of data points, data points corresponding to a specified interval of the immediately preceding first and second myoelectric signals,

means for comparing said second plurality of data points with said first plurality of data points every time a pair of data points is converted, and

means for determining the deviation of said second plurality of data points from said first plurality of data points, and

means for switching degrees of freedom of said prosthesis responsive to said deviation being less than a specified value.