Self calibrating linear position sensor

• US 6,190,319 B1
• Filed: 06/21/1999
• Issued: 02/20/2001
• Est. Priority Date: 06/21/1999
• Status: Expired due to Term

• Current Assignee: Uniloc 2017 LLC (FIG LLC (d/b/a Fortress Investment Group LLC))
• Original Assignee: International Business Machines Corporation
• Inventors: Goldowsky, Michael Philip
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): Imam, Ali M.
• Application Number:
  US09/334,504
• Time in Patent Office: 610 Days
• Field of Search: 600/16, 600/17, 600/437, 600/443, 600/447, 600/449, 736/18, 736/19, 736/25, 736/26, 436/68, 324/227
• US Class Current: 600/437
• CPC Class Codes: A61M 60/148 in line with a blood vessel using resection or like techniques, e.g. permanent endovascular heart assist devices
• CPC Class Codes: A61M 60/178 drawing blood from a ventricle and returning the blood to the arterial system via a cannula external to the ventricle, e.g. left or right ventricular assist devices
• CPC Class Codes: A61M 60/422 the force acting on the blood contacting member being electromagnetic, e.g. using canned motor pumps
• CPC Class Codes: A61M 60/816 Sensors arranged on or in the housing, e.g. ultrasound flow sensors
• CPC Class Codes: A61M 60/824 Hydrodynamic or fluid film bearings
• CPC Class Codes: A61M 60/894 Passive valves, i.e. valves actuated by the blood

Abstract

A rotor is disposed coaxially in a tubular housing and spaced therefrom to define a gap for receiving a fluid. An ultrasonic transducer is mounted at one end of the housing in alignment with a target at a corresponding end of the rotor. Ultrasonic pulses are bounced off the target for measuring linear position thereof based on the speed of sound in the fluid and round trip pulse time between the transducer and target. The speed of sound in the fluid between the transducer and target is self-calibrated.

Claims

1. An apparatus comprising:

a tubular housing;

a rotor disposed coaxially in said housing and spaced radially inwardly therefrom to define a gap therebetween for receiving a fluid, and including a target at one end thereof;

an ultrasonic transducer mounted at a first end of said housing in alignment with said target for bouncing ultrasonic pulses thereoff for measuring linear position thereof based on the speed of sound in said fluid and the round trip pulse time between said transducer and target; and

means for calibrating said speed of sound in said fluid from a predetermined calibration dimension between said transducer and target.

2. An apparatus according to claim 1 wherein calibrating means comprise:

a feature of said rotor having said predetermined calibration dimension relative to said target; and

a processor operatively joined to said transducer for calculating said speed of sound in said fluid based on said target position, said calibration dimension, and said round trip pulse time.

3. An apparatus according to claim 2 wherein:

said calibration feature comprises an end face of said rotor at an axial second end thereof opposite to said target, with said calibration dimension being axial length of said rotor therebetween; and

said calibrating means are configured to hold said rotor end face at a corresponding opposite second end of said housing for measuring said linear position of said target by said transducer.

4. An apparatus according to claim 2 wherein:

said calibration feature comprises an end face of said rotor at an axial second end thereof opposite to said target, with said calibration dimension being axial length of said rotor therebetween;

said calibrating means further comprise a second ultrasonic transducer operatively joined to said processor opposite to said first transducer in alignment with said rotor end face for bouncing second ultrasonic pulses thereoff for measuring linear position thereof; and

said processor is configured for calculating said speed of sound in said fluid based on said positions of said rotor target and end face, said rotor axial length, and said respective round trip pulse times.

5. An apparatus according to claim 2 wherein:

said target comprises a flat annulus at said rotor first end; and

said calibrating feature is a local step in said target, and said calibration dimension is axial offset of said step from said target.

6. An apparatus according to claim 5 wherein said calibration feature comprises a plurality of said steps circumferentially spaced apart from each other around said target.

7. An apparatus according to claim 6 wherein said steps comprise pads extending axially outwardly from said target.

8. An apparatus according to claim 6 wherein said steps comprise slots extending axially inwardly from said target.

9. An apparatus according to claim 6 wherein said processor is configured for calculating said linear position of said target based on said round trip times of said pulses transmitted from said transducer, and resolving rotary motion of said rotor based on changes in said round trip pulse times circumferentially around said steps.

10. An apparatus according to claim 9 further comprising:

means for axially reciprocating said rotor inside said housing; and

means for rotating said rotor inside said housing.

11. An apparatus according to claim 10 wherein:

said target is co-radial with said steps and circumferentially interrupted thereby; and

said transducer is aligned with said rotor to intercept said steps and target in turn as said rotor rotates.

12. An apparatus according to claim 11 wherein said processor includes a low pass filter for resolving said target linear position from said transducer, and a high pass filter for resolving said rotary motion from said transducer.

13. An apparatus according to claim 10 wherein:

said target is a continuous annulus disposed radially inwardly of said steps; and

said transducer is aligned with said rotor to intercept said steps and target each in part as said rotor rotates.

14. An apparatus according to claim 13 wherein said processor is configured to resolve said linear position and rotary motion from said transducer without filtering therefor.

15. An apparatus according to claim 10 wherein:

said rotor comprises a piston for pumping blood fluid through said housing; and

said processor is operatively joined to said reciprocating and rotating means for controlling movement of said piston and flow of said blood through said housing.

16. A method of measuring linear position of a rotor disposed inside a housing in a fluid comprising:

bouncing from said housing ultrasonic pulses off a target at a first end of said rotor and through said fluid for measuring linear position of said target in said housing based on the product of speed of sound in said fluid and round trip times of said bounced pulses along a pulse path between said housing and target; and

calibrating said speed of sound in said fluid from a predetermined calibration dimension along said pulse path.

17. A method according to claim 16 wherein said speed of sound calibration comprises:

providing said predetermined calibration dimension in said rotor relative to said target;

bouncing said pulses through said fluid and off said target to measure said linear position thereof; and

calculating said speed of sound in said fluid based on said target position, said calibration dimension, and said round trip pulse time.

18. A method according to claim 17 wherein said speed of sound calibration further comprises:

holding said rotor at one end of said housing;

bouncing said pulse off said target at an opposite end of said housing for measuring said target position; and

calculating said speed of sound in said fluid based on said target position and said round trip pulse time.

19. A method according to claim 17 wherein said speed of sound calibration further comprises:

bouncing corresponding ultrasonic pulses off both said target at one end of said rotor, and off an end face at an opposite end of said rotor to obtain respective round trip times thereof; and

calculating said speed of sound in said fluid based on linear positions of said target and end face, and said respective round trip pulse times.

20. A method according to claim 17 further comprising:

providing a local step in said target to define said calibration dimension therebetween;

bouncing said pulses in turn off said target and step as said rotor rotates and translates inside said housing for measuring linear positions thereof; and

calibrating said speed of sound from the difference in round trip pulse times between the linear positions of said target and step.

21. A method according to claim 20 further comprising:

providing a plurality of said steps circumferentially spaced apart from each other around said target;

bouncing said pulses off said target and steps as said rotor rotates and translates inside said housing 16 for measuring linear positions thereof; and

resolving rotary motion of said rotor based on changes in said round trip pulse times circumferentially around said steps.

22. A method according to claim 21 wherein:

said pulses are bounced off said target and steps in turn as said rotor rotates; and

said linear position and rotary motion of said rotor are resolved by filtering said pulses bounced from said target and steps.

23. A method according to claim 21 wherein:

said pulses are bounced in part off said target and in part off said steps in turn; and

said linear position and rotary motion of said rotor are resolved independently.